project.config: explicitly grant tag creation to golang-gob-owners

I didn't think this would be necessary, but perhaps Administrate Server is more limited than I thought it is.

Change-Id: I234aeb39c4a7a6a13f62a1aaaf095ee4303f9785
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/488395
Reviewed-by: Michael Pratt <mpratt@google.com>
diff --git a/project.config b/project.config
index 566d03a..3211cbc 100644
--- a/project.config
+++ b/project.config
@@ -64,7 +64,9 @@
 	push = group mdb/golang-gob-owners
 [access "refs/tags/*"]
 	create = group gobot
+	create = group mdb/golang-gob-owners
 	createTag = group gobot
+	createTag = group mdb/golang-gob-owners
 [access "^refs/heads/(release|internal)-branch.+"]
 	exclusiveGroupPermissions = label-Auto-Submit submit
 	submit = group gobot