Explicitly load GCC 15.2 when necessary

Author: knoepfel

.github/workflows/cmake-build.yaml

@@ -215,6 +215,12 @@ jobs:
       id: repo_name
       run: echo "name=$(echo '${{ needs.pre-check.outputs.repo }}' | sed 's:.*/::')" >> "$GITHUB_OUTPUT"
 
+    - name: Load Spack-installed GCC
+      if: matrix.compiler == 'gcc'
+      run: |
+        . /entrypoint.sh
+        spack load gcc@15.2
+
     - name: Configure CMake
       id: configure
       uses: Framework-R-D/phlex/.github/actions/configure-cmake@main