fix(ci): restore cancel-in-progress on prerelease builds

Hourly polling is sufficient to prevent re-dispatch during builds.
Keep cancel-in-progress: true so stalled builds can be cleared.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-prerelease.yml

@@ -22,7 +22,7 @@ on:
 
 concurrency:
   group: prerelease-build
-  cancel-in-progress: false
+  cancel-in-progress: true
 
 jobs:
   build: