Add missing "initialize-julia" in pixi tasks

[visr]

This allowed it to pick up Julia 1.11, leading to #1883.

[visr]

I'll close this in favor of #1890. Since Pkg,test takes care of environment initialization anyway, and uses different precompile files, this does a bunch of extra work that we don't need. For the quarto-render job it could be useful, but that is mainly used in CI and there it is preceded by install-ci already.