ci: drop the dev branch trigger from cpp-tests, doc-build, markdown-links

The dev branch has been removed (trunk-based workflow: push to main, use
short-lived feature branches + PRs for risky/reviewable changes). These three
workflows still listed 'dev' as a push trigger — a dead reference now that the
branch is gone. Removed so the CI config matches reality.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/markdown-links.yml

@@ -14,7 +14,6 @@ on:
   push:
     branches:
       - main
-      - dev
       - "claude/**"
       - "feature/**"
       - "review/**"