Add proper CI job for building with minimum dependency versions

We have repeatedly been impacted by more recent versions of dependencies
requiring more recent versions of Rust in our CI workflow that tests
building with the minimum supported Rust version. That is mostly the
case because we do not lock our dependent versions via a Cargo.lock
file.
In order to prevent any issues from this setup, this change introduces a
proper CI job that makes sure to compile against the minimum versions of
dependencies with the minimum Rust version we support.

.github/workflows/test.yml

@@ -20,12 +20,12 @@ env:
 
 jobs:
   test:
-    name: Build and test [${{ matrix.rust }}, ${{ matrix.profile }}]
+    name: Build and test [${{ matrix.profile }}]
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.60.0, stable]
+        rust: [stable]
         profile: [dev, release]
     steps:
     - uses: actions/checkout@v3
@@ -38,6 +38,27 @@ jobs:
       run: |
         cargo build --profile=${{ matrix.profile }} --bins
         cargo test --profile=${{ matrix.profile }}
+  build-minimum:
+    name: Build using minimum versions of dependencies
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Nightly Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+      - run: cargo +nightly -Z minimal-versions update
+      - name: Install minimum Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          # Please adjust README and rust-version field in Cargo.toml files when
+          # bumping version.
+          toolchain: 1.60.0
+          default: true
+      - name: Build
+        run: cargo build --features=vendored-openssl --locked
   clippy:
     name: Lint with clippy
     runs-on: ubuntu-latest

Cargo.toml

@@ -55,3 +55,10 @@ tracing = {version = "0.1", default-features = false, features = ["std"]}
 tracing-subscriber = {version = "0.3", default-features = false, features = ["ansi", "env-filter", "fmt"]}
 uuid = {version = "1.0", features = ["v4"]}
 yansi = {version = "0.5", default-features = false}
+
+[dev-dependencies]
+# A set of unused dependencies that we require to force correct minimum versions
+# of transitive dependencies, for cases where our dependencies have incorrect
+# dependency specifications themselves.
+_rustc_version_unused = { package = "rustc_version", version = "0.2.2" }
+_num_bigint_unused = { package = "num-bigint", version = "0.4.2" }