Bump push action to 2.8.0

This fixes the build/push action to assume that the Dockerfile is
relative to `context`

Author: brianhlin

action.yml

@@ -86,7 +86,7 @@ runs:
       password: ${{ inputs.registry_pass }}
 
   - name: Build image
-    uses: docker/build-push-action@v2.2.2
+    uses: docker/build-push-action@v2.8.0
     with:
       push: true
       context: ${{ inputs.context }}