Don't rely on juliaup override for version selection

We have

```
install-julia = "juliaup add 1.10.5 && juliaup override unset && juliaup override set 1.10.5"
```

But in #1883 we can see (@evetion can see) that the Julia tests are still run using Julia 1.11, which is the new stable release that came out today.

Rather than trying to find out what exactly goes wrong with the override, this just sets it when we start julia, so we can release.

pixi.toml

@@ -30,9 +30,9 @@ install = { depends_on = [
  "install-pre-commit",
 ] }
 # Julia
-update-registry-julia = "julia --eval='using Pkg; Registry.update()'"
-update-manifest-julia = "julia --project --eval='using Pkg; Pkg.update()'"
-instantiate-julia = { cmd = "julia --project --eval='using Pkg; Pkg.instantiate()'", env = { JULIA_SSL_CA_ROOTS_PATH = "" } }
+update-registry-julia = "julia +1.10.5 --eval='using Pkg; Registry.update()'"
+update-manifest-julia = "julia +1.10.5 --project --eval='using Pkg; Pkg.update()'"
+instantiate-julia = { cmd = "julia +1.10.5 --project --eval='using Pkg; Pkg.instantiate()'", env = { JULIA_SSL_CA_ROOTS_PATH = "" } }
 initialize-julia = { depends_on = [
  "update-registry-julia",
  "instantiate-julia",
@@ -49,7 +49,7 @@ quarto-preview = { cmd = "quarto preview docs", depends_on = [
  "generate-testmodels",
 ] }
 quarto-check = { cmd = "quarto check all", depends_on = ["quartodoc-build"] }
-quarto-render = { cmd = "julia --project --eval 'using Pkg; Pkg.build(\"IJulia\")' && quarto render docs --to html --execute", depends_on = [
+quarto-render = { cmd = "julia +1.10.5 --project --eval 'using Pkg; Pkg.build(\"IJulia\")' && quarto render docs --to html --execute", depends_on = [
  "quartodoc-build",
  "generate-testmodels",
 ] }
@@ -67,21 +67,21 @@ lint = { depends_on = [
  "mypy-ribasim-qgis",
 ] }
 # Build
-build = { "cmd" = "julia --project build.jl", cwd = "build", depends_on = [
+build = { "cmd" = "julia +1.10.5 --project build.jl", cwd = "build", depends_on = [
  "generate-testmodels",
  "initialize-julia",
 ], env = { JULIA_SSL_CA_ROOTS_PATH = "" } }
-remove-artifacts = "julia --eval 'rm(joinpath(Base.DEPOT_PATH[1], \"artifacts\"), force=true, recursive=true)'"
+remove-artifacts = "julia +1.10.5 --eval 'rm(joinpath(Base.DEPOT_PATH[1], \"artifacts\"), force=true, recursive=true)'"
 # Tests
 test-ribasim-cli = "pytest --numprocesses=4 --basetemp=build/tests/temp --junitxml=report.xml build/tests"
-test-ribasim-core = { cmd = "julia --project=core --eval 'using Pkg; Pkg.test()'", depends_on = [
+test-ribasim-core = { cmd = "julia +1.10.5 --project=core --eval 'using Pkg; Pkg.test()'", depends_on = [
  "generate-testmodels",
 ] }
 test-ribasim-migration = { cmd = "pytest --numprocesses=4 -m regression python/ribasim/tests" }
-test-ribasim-core-cov = { cmd = "julia --project=core --eval 'using Pkg; Pkg.test(coverage=true, julia_args=[\"--check-bounds=yes\"])'", depends_on = [
+test-ribasim-core-cov = { cmd = "julia +1.10.5 --project=core --eval 'using Pkg; Pkg.test(coverage=true, julia_args=[\"--check-bounds=yes\"])'", depends_on = [
  "generate-testmodels",
 ] }
-test-ribasim-regression = { cmd = "julia --project=core --eval 'using Pkg; Pkg.test(julia_args=[\"--check-bounds=yes\"], test_args=[\"regression\"])'", depends_on = [
+test-ribasim-regression = { cmd = "julia +1.10.5 --project=core --eval 'using Pkg; Pkg.test(julia_args=[\"--check-bounds=yes\"], test_args=[\"regression\"])'", depends_on = [
  "generate-testmodels",
  "test-ribasim-migration",
 ] }
@@ -94,9 +94,9 @@ generate-testmodels = { cmd = "python utils/generate-testmodels.py", inputs = [
 ] }
 tests = { depends_on = ["lint", "test-ribasim-python", "test-ribasim-core"] }
 delwaq = { cmd = "pytest python/ribasim/tests/test_delwaq.py" }
-model-integration-test = { cmd = "julia --project=core --eval 'using Pkg; Pkg.test(test_args=[\"integration\"])'" }
+model-integration-test = { cmd = "julia +1.10.5 --project=core --eval 'using Pkg; Pkg.test(test_args=[\"integration\"])'" }
 # Codegen
-codegen = { cmd = "julia --project utils/gen_python.jl && ruff format python/ribasim/ribasim/schemas.py python/ribasim/ribasim/validation.py", depends_on = [
+codegen = { cmd = "julia +1.10.5 --project utils/gen_python.jl && ruff format python/ribasim/ribasim/schemas.py python/ribasim/ribasim/validation.py", depends_on = [
  "initialize-julia",
 ], inputs = [
  "core",
@@ -143,10 +143,10 @@ test-ribasim-qgis-cov = { cmd = "pytest --numprocesses=auto --cov=ribasim_qgis -
 ] }
 mypy-ribasim-qgis = "mypy ribasim_qgis"
 # Run
-ribasim-core = { cmd = "julia --project=core -e 'using Ribasim; Ribasim.main(ARGS)'", depends_on = [
+ribasim-core = { cmd = "julia +1.10.5 --project=core -e 'using Ribasim; Ribasim.main(ARGS)'", depends_on = [
  "initialize-julia",
 ] }
-ribasim-core-testmodels = { cmd = "julia --project --threads=4 utils/testmodelrun.jl", depends_on = [
+ribasim-core-testmodels = { cmd = "julia +1.10.5 --project --threads=4 utils/testmodelrun.jl", depends_on = [
  "generate-testmodels",
  "initialize-julia",
 ] }