Add gcc 15 to CI

Author: andreasbuhr

.github/workflows/cmake.yml

@@ -527,15 +527,15 @@ jobs:
     - name: Create Build Environment
       # Some projects don't allow in-source building, so create a separate build directory
       # We'll use this as our working directory for all subsequent commands
-      # Use github.workspace since only this path is mounted inside containers
-      run: cmake -E make_directory ${{ github.workspace }}/build
+      # Use the GITHUB_WORKSPACE env var so the path resolves correctly inside containers (/__w/...)
+      run: cmake -E make_directory "$GITHUB_WORKSPACE/build"
 
     - name: Configure CMake
       if: (!contains(matrix.config.mingw, 'MINGW'))
       # Use a bash shell so we can use the same syntax for environment variable
       # access regardless of the host operating system
       shell: bash
-      working-directory: ${{ github.workspace }}/build
+      working-directory: $GITHUB_WORKSPACE/build
       env: 
         CXX: ${{ matrix.config.cxx }}
       # Note the current convention is to use the -S and -B options here to specify source 
@@ -555,14 +555,14 @@ jobs:
 
     - name: Build
       if: (!contains(matrix.config.mingw, 'MINGW'))
-      working-directory: ${{ github.workspace }}/build
+      working-directory: $GITHUB_WORKSPACE/build
       shell: bash
       # Execute the build.  You can specify a specific target with "--target <NAME>"
       run: cmake --build . --config ${{ matrix.config.buildtype }}
 
     - name: Test
       if: (!contains(matrix.config.mingw, 'MINGW'))
-      working-directory: ${{ github.workspace }}/build
+      working-directory: $GITHUB_WORKSPACE/build
       shell: bash
       # Execute tests defined by the CMake configuration.  
       # See https://cmake.org/cmake/help/latest/manual/ctest.1.html for more detail