Fix image release workflow (#27)

* Specify image tag correctly

See: https://github.com/storageos/init/actions/runs/2033605430

* Rename file

.github/workflows/releas-image.yml → .github/workflows/release-image.yml

@@ -14,10 +14,10 @@ jobs:
         uses: actions/checkout@v2
       - name: Set image tag env var
         # Refer https://stackoverflow.com/a/58178121 for git tag extraction.
-        run: echo "IMAGE=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
+        run: echo "IMAGE_TAG=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
       - name: Set image env vars
         run: |
-          echo "IMAGE=storageos/init:${{ env.OPERATOR_IMAGE_TAG }}" >> $GITHUB_ENV
+          echo "IMAGE=storageos/init:${{ env.IMAGE_TAG }}" >> $GITHUB_ENV
       - name: Login to docker container registry
         uses: docker/login-action@v1
         with: