Fix image bundle hash key calculation

The hash calculation did not take the image bundle list into account.

String interpolation only works in "YAML" mode. If you are already in
"script" mode, you need to use different techniques. This explains why
the image bundle list was never picked up and why image bundles with the
wrong content were shared between builds.

Fixes: 4fc896e ("Unify Airgap and IPv6 test image build workflows")
Signed-off-by: Tom Wieczorek <[email protected]>
(cherry picked from commit 991ec04)

Author: twz123

.github/workflows/build-image-bundle.yml

@@ -56,7 +56,7 @@ jobs:
       - name: "Cache :: Image bundle :: Calculate cache key"
         id: cache-image-bundle-calc-key
         env:
-          HASH_VALUE: ${{ hashFiles('Makefile', '${{ inputs.image-bundle-name }}-images.txt', 'cmd/airgap/*', 'pkg/airgap/*') }}
+          HASH_VALUE: ${{ hashFiles('Makefile', format('{0}-images.txt', inputs.image-bundle-name), 'cmd/airgap/*', 'pkg/airgap/*') }}
         run: |
           printf 'cache-key=build-%s-image-bundle-%s-%s-%s\n' "$IMAGE_BUNDLE_NAME" "$TARGET_OS" "$TARGET_ARCH" "$HASH_VALUE" >> "$GITHUB_OUTPUT"