fix: remove clean:false from CI checkout (stale workspace failures)

The clean:false setting causes checkout to fail when previous runs
leave corrupted workspaces. Default clean behavior ensures fresh
checkout each run.

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

.gitea/workflows/build-iso-dev.yml

@@ -14,7 +14,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 1
-          clean: false
 
       - name: Install ISO build dependencies
         run: |