fix: build docker script checks whether the github event is a tag push

build_docker.sh

@@ -5,8 +5,7 @@ version=$(git describe --tags --always | sed 's/^v//')
 # note: we may want to extend this to also not tag as latest if working tree is dirty.
 # but i think because of how go bindata works, it probably makes a change in the working tree.
 tag=master
-BRANCH=${GITHUB_HEAD_REF:-${GITHUB_REF_NAME:-$(git branch --show-current)}}
-[[ "$BRANCH" == "master" ]] && [[ "$version" != *-* ]] && tag=latest
+[[ "$GITHUB_EVENT_NAME" = "push" ]] && [[ "$GITHUB_REF_TYPE" = "tag" ]] && [[ "$version" != *-* ]] && tag=latest
 
 
 docker build --tag=grafana/carbon-relay-ng:$tag .