Add a job to test the MSRV of ctest

Only `libc` is checked with 1.63 normally. Add a job that verifies the
same for `ctest`.

Author: tgross35

.github/workflows/ci.yaml

@@ -213,6 +213,23 @@ jobs:
             export PATH=$HOME/.rust_solaris/bin:$PATH
             ./ci/run.sh ${{ matrix.target }}
 
+  ctest_msrv:
+    name: Check MSRV
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    env:
+      RUSTFLAGS: # No need to check warnings on old MSRV, unset `-Dwarnings`
+    steps:
+    - uses: actions/checkout@master
+    - run: |
+        msrv="$(perl -ne 'print if s/rust-version\s*=\s*"(.*)"/\1/g' ctest/Cargo.toml)"
+        echo "MSRV: $msrv"
+        echo "MSRV=$msrv" >> "$GITHUB_ENV"
+    - name: Install Rust
+      run: rustup update "$MSRV" --no-self-update && rustup default "$MSRV"
+    - uses: Swatinem/rust-cache@v2
+    - run: cargo build -p ctest
+
   # One job that "summarizes" the success state of this pipeline. This can then be added to branch
   # protection, rather than having to add each job separately.
   success:
@@ -224,6 +241,7 @@ jobs:
       - test_tier2
       - test_tier2_vm
       - verify_build
+      - ctest_msrv
     # Github branch protection is exceedingly silly and treats "jobs skipped because a dependency
     # failed" as success. So we have to do some contortions to ensure the job fails if any of its
     # dependencies fails.