meta: do not create tag when there are no public changes

.github/scripts/tag.sh

@@ -2,12 +2,28 @@
 
 set -e
 
+tag_has_public_changes=false
+
+previous_tag=$(git describe --tags --abbrev=0 HEAD~)
+
+# Loop through all commits since previous tag
+for rev in $(git log "$previous_tag"..HEAD --format="%H" --reverse --no-merges); do
+    summary=$(git log "$rev"~.."$rev" --format="%s")
+    # Exclude commits starting with "Meta"
+    if [[ $summary != Meta* ]]; then
+        tag_has_public_changes=true
+        break
+    fi
+done
+
 head_tag=$(git describe --exact-match 2>/dev/null || true)
 
 git log --color=always --format="%C(auto)%h %s%d" | head
 
-if [[ ${head_tag} =~ [\d{2}\.\d{2}\.\d+] ]]
-then
+if ! $tag_has_public_changes; then
+    echo "No public changes since $previous_tag." >&2
+    exit 1
+elif [[ ${head_tag} =~ [\d{2}\.\d{2}\.\d+] ]]; then
     echo "Version tag ${head_tag} already exists."
 else
     git config --local user.email "[email protected]"