ci(update-pkgver): only trigger on package-relevant paths

Workflow had no path filter — every push to main fired the pkgver-bump
which in turn triggered the heavy build-and-publish pipeline in
moonarch-pkgbuilds, even for changes that the moonarch-git PKGBUILD
does not package: README/DECISIONS edits, post-install.sh, lib.sh,
or workflow tweaks themselves.

Restrict the trigger to defaults/, packages/, and the two scripts
that PKGBUILD actually installs (moonarch-update, moonarch-doctor).
Comment lists explicitly what the filter excludes so the next reader
doesn't have to reverse-engineer it.

.gitea/workflows/update-pkgver.yaml

@@ -7,6 +7,15 @@ on:
   push:
     branches:
       - main
+    paths:
+      # Only files that the moonarch-git PKGBUILD actually packages.
+      # README.md, DECISIONS.md, scripts/post-install.sh, scripts/lib.sh,
+      # CI workflow edits, etc. don't change the built package and must
+      # not trigger a rebuild.
+      - 'defaults/**'
+      - 'packages/**'
+      - 'scripts/moonarch-update'
+      - 'scripts/moonarch-doctor'
 
 jobs:
   update-pkgver: