fix: avoid SIGPIPE in changelog step by using grep -m 1

Replacing head -1 (and the broken head -2|tail -1 attempt) with grep -m 1
stops grep after the first match, eliminating the SIGPIPE that caused exit 141.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Generate changelog
         id: changelog
         run: |
-          PREV_TAG=$(git tag --sort=-version:refname | grep -v "^${GITHUB_REF#refs/tags/}$" | head -1)
+          PREV_TAG=$(git tag --sort=-version:refname | grep -m 1 -v "^${GITHUB_REF#refs/tags/}$")
           if [ -n "$PREV_TAG" ]; then
             CHANGELOG=$(git log --pretty=format:"- %s" "${PREV_TAG}..HEAD")
           else