feat: test building the docker image when building a non-release

contrib/release-dokku

@@ -363,7 +363,8 @@ fn-build-docker-image() {
     docker buildx build \
       --platform linux/arm/v7,linux/arm64/v8,linux/amd64 \
       --progress plain \
-      --tag "dokku/dokku:$VERSION" .
+      --tag "dokku/dokku:latest" \
+      --tag "dokku/dokku:$(echo "$VERSION" | tr + -)" .
   fi
 }
 
@@ -422,6 +423,8 @@ main() {
     fn-build-docker-image "$NEXT_VERSION" "$IS_RELEASE" || log-fail "Error building docker image"
 
     fn-repo-push-tags "$IS_RELEASE"
+  else
+    fn-build-docker-image "$NEXT_VERSION" "$IS_RELEASE" || log-fail "Error building docker image"
   fi
 
   if [[ "$IS_RELEASE" != "true" ]]; then