GitHubCI(publish): only consider tags that start with 'v'

It turns out that this was the standard for all previous
tags but somehow I missed when tagging 0.21.2, d'oh!

By doing this, if I make the same mistake again, the workflow
won't start and no release will happen (until I push the
proper tag).

Author: knocte

.github/workflows/publish.yml

@@ -3,7 +3,7 @@ name: Publish
 on:
   push:
     tags:
-      - '*' # Publish on any new tag
+      - 'v*' # Publish on any new tag
 
 jobs:
   build: