CI: only login to ghcr.io for building matrix-tools if we're on a tag

Author: benbz

.github/workflows/matrix-tools.yml

@@ -59,6 +59,7 @@ jobs:
       uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4
 
     - name: Login to GHCR
+      if: ${{ github.ref_type == 'tag' }}
       uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772  # v3
       with:
         registry: ghcr.io