Try fetching entire history?

.github/workflows/check-image-metadata.yaml

@@ -17,6 +17,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - uses: DeterminateSystems/nix-installer-action@v14
       - uses: DeterminateSystems/magic-nix-cache-action@v8
       - name: Print variables
@@ -26,4 +28,4 @@ jobs:
           echo "github.ref = '${{ github.ref }}'"
       - name: Check image metadata
         run: |
-          nix develop --command nu check-image-metadata.nu --git-diff '{"source": "origin/${{ github.head_ref }}", "target": "origin/${{ github.base_ref }}"}'
+          nix develop --command nu check-image-metadata.nu --git-diff '{"source": "${{ github.ref }}", "target": "${{ github.base_ref }}"}'