ci: Use the right cache key on Windows

Author: jorisv

.github/workflows/windows-conda.yml

@@ -46,8 +46,8 @@ jobs:
     - uses: actions/cache@v4
       with:
         path: .ccache
-        key: ccache-windows-conda-${{ matrix.os }}-${{ github.sha }}
-        restore-keys: ccache-windows-conda-${{ matrix.os }}-
+        key: ccache-windows-conda-${{ matrix.compiler }}-${{ matrix.os }}-${{ github.sha }}
+        restore-keys: ccache-windows-conda-${{ matrix.compiler }}-${{ matrix.os }}-
 
     - uses: conda-incubator/setup-miniconda@v3
       with: