Remove GitHub slug action (#14412)

It's used for tagging containers, but we don't believe anything relies
on these tags. The SHA is still available as a tag for identifying
images if necessary.

Author: JamieB-gu

.github/workflows/container.yml

@@ -19,9 +19,6 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
-      - name: Inject slug/short variables
-        uses: rlespinasse/[email protected]
-
       - name: Set up Node environment
         uses: ./.github/actions/setup-node-env
 
@@ -39,7 +36,7 @@ jobs:
         uses: redhat-actions/[email protected]
         with:
           image: dotcom-rendering
-          tags: ${{ github.sha }} ${{ env.GITHUB_REF_SLUG }}
+          tags: ${{ github.sha }}
           context: ./
           containerfiles: ./dotcom-rendering/Containerfile