scripts/update-gh-pages: fix release version parsing

When determining the release branch only consider "main" release tags,
refusing to pick api/nfd/v* tags.

(cherry picked from commit a416af5)

scripts/github/update-gh-pages.sh

@@ -105,7 +105,7 @@ site_subdir=${site_subdir:-master}
 
 # Check if this ref is for a released version
 if [ "$site_subdir" != "master" ]; then
-    _base_tag=`git describe --abbrev=0 || :`
+    _base_tag=`git describe --abbrev=0 --match "v*" || :`
     case "$_base_tag" in
         $site_subdir*)
             ;;