Check image GitHub Action fix to remove ENV variable (project-koku#4097)

* Fix skopeo error with ENV variable

.github/workflows/check-image.yml

@@ -14,7 +14,7 @@ jobs:
         run: sudo apt-get install -y skopeo
       - name: Check change
         run: |
-          BASE_IMAGE="registry.access.redhat.com/ubi8/ubi-minimal:latest" skopeo inspect "docker://${BASE_IMAGE}" | grep -Po '(?<="Digest": ")([^"]+)' > .baseimagedigest
+          skopeo inspect "docker://registry.access.redhat.com/ubi8/ubi-minimal:latest" | grep -Po '(?<="Digest": ")([^"]+)' > .baseimagedigest
           docker run --rm --entrypoint sh -u 0 quay.io/cloudservices/koku:latest -c \
             'yum upgrade -y --security > /dev/null; rpm -qa | sort | sha256sum' \
             >> .baseimagedigest