sync-tags: temporarily publish only alpha tags

This commit restricts publishing to only alpha tags for now, just as a
safety check so that we can verify and thoroughly test importing repos
with v0.18.0-alpha.1 before turning it on for v0.17.0.

Author: nikhita

cmd/sync-tags/main.go

@@ -183,6 +183,11 @@ func main() {
 	// create or update tags from kTagCommits as local tags with the given prefix
 	createdTags := []string{}
 	for name, kh := range kTagCommits {
+		// temporarily publish only alpha tags
+		if !strings.Contains(name, "alpha") {
+			continue
+		}
+
 		bName := name
 		if *prefix != "" {
 			bName = *prefix + name[1:] // remove the v