ci: Only update caches from main repository

Forks are not allowed to update the cache

.github/workflows/knut-tests.yml

@@ -123,7 +123,7 @@ jobs:
       - name: "Delete previous compiler cache"
         # Updating th cache doesn't work from forks
         # So update it once it's merged into the repo
-        if: ${{ steps.compiler-cache-restore.outputs.cache-hit }}
+        if: ${{ steps.compiler-cache-restore.outputs.cache-hit &&  github.event_name == 'push' }}
         continue-on-error: true
         run: |
           gh extension install actions/gh-actions-cache
@@ -132,6 +132,9 @@ jobs:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       - name: "Save Compiler Cache"
         uses: actions/cache/save@v4
+        # Updating th cache doesn't work from forks
+        # So update it once it's merged into the repo
+        if: ${{ github.event_name == 'push' }}
         with:
           path: ${{ matrix.compiler_cache_path }}
           key: ${{ matrix.os }}_compiler_cache