Test the oldest supported CMake version in CI

.github/workflows/ci.yaml

@@ -88,6 +88,17 @@ jobs:
       - run: (cd build && ctest -C Debug )
         if: startsWith(matrix.os, 'windows')
 
+  oldest-supported-cmake:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: true
+      # Installing 3.11.4.post1 through 3.13.3 fail for various reasons, so 3.14
+      # is the oldest version we can reasonably test.
+      - run: pipx install cmake==3.14.4.post1 && cmake --version
+      - run: cmake -Wdev -Werror=dev -S . -B build
+
 concurrency:
   group: ${{ github.head_ref || github.run_id }}
   cancel-in-progress: true