Docker: Add pre-release tag (#6470)

https://github.com/XTLS/Xray-core/pull/6470#issuecomment-4947190027

---------

Co-authored-by: KobeArthurScofield <26771058+KobeArthurScofield@users.noreply.github.com>
Co-authored-by: Meow <197331664+Meo597@users.noreply.github.com>

.github/workflows/docker.yml

@@ -64,6 +64,14 @@ jobs:
           echo "Latest: '$LATEST'."
           echo "LATEST=$LATEST" >>${GITHUB_ENV}
 
+          NEWEST=false
+          if [[ "${{ github.event_name }}" == "release" ]]; then
+            NEWEST=true
+          fi
+
+          echo "Newest: '$NEWEST'."
+          echo "NEWEST=$NEWEST" >>${GITHUB_ENV}
+
       - name: Checkout code
         uses: actions/checkout@v7
 
@@ -124,6 +132,13 @@ jobs:
             ${{ env.FULL_IMAGE_NAME }}:${{ env.IMAGE_TAG }}
           fi
 
+          if [[ "${{ env.NEWEST }}" == "true" ]]; then
+            echo "Adding 'pre-release' tag to manifest: '${{ env.FULL_IMAGE_NAME }}:pre-release'."
+            docker buildx imagetools create \
+            --tag ${{ env.FULL_IMAGE_NAME }}:pre-release \
+            ${{ env.FULL_IMAGE_NAME }}:${{ env.IMAGE_TAG }}
+          fi
+
       - name: Inspect image
         run: |
           docker buildx imagetools inspect ${{ env.FULL_IMAGE_NAME }}:${{ env.IMAGE_TAG }}
@@ -131,3 +146,7 @@ jobs:
           if [[ "${{ env.LATEST }}" == "true" ]]; then
             docker buildx imagetools inspect ${{ env.FULL_IMAGE_NAME }}:latest
           fi
+
+          if [[ "${{ env.NEWEST }}" == "true" ]]; then
+            docker buildx imagetools inspect ${{ env.FULL_IMAGE_NAME }}:pre-release
+          fi