ci(coverage): simplify coverage step and pin shell to bash

- removes unreachable `; exit ${PIPESTATUS[0]}` — already covered by pipefail (Tobias)
- adds explicit `shell: bash` to both new steps for clarity (Tobias)

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

.gitea/workflows/ci.yml

@@ -43,12 +43,14 @@ jobs:
           TZ: Europe/Berlin
 
       - name: Run coverage (server + client)
-        run: npm run test:coverage 2>&1 | tee /tmp/coverage-test.log; exit ${PIPESTATUS[0]}
+        shell: bash
+        run: npm run test:coverage 2>&1 | tee /tmp/coverage-test.log
         working-directory: frontend
         env:
           TZ: Europe/Berlin
 
       - name: Assert no birpc teardown race in coverage run
+        shell: bash
         if: always()
         run: |
           if grep -q "rpc is closed" /tmp/coverage-test.log 2>/dev/null; then