Remove untagged docker versions (paritytech#20)

* Remove untagged docker versions

* Do not run docker on PR

.github/workflows/docker.yml

@@ -60,8 +60,9 @@ jobs:
           images: |
             ghcr.io/subcoin-project/subcoin
           tags: |
-            type=ref,event=tag
             type=ref,event=branch
+            type=ref,event=tag
+            type=sha
           flavor: |
             latest=false
             suffix=${{ matrix.platform.image-suffix }}
@@ -77,6 +78,9 @@ jobs:
           push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          # Added to prevent tons of untagged images in GHCR.
+          # See: https://github.com/docker/build-push-action/issues/894
+          provenance: false
           build-args: |
             SUBSTRATE_CLI_GIT_COMMIT_HASH=${{ github.sha }}
             PROFILE=${{ matrix.platform.profile }}