CI: Set a timeout for the test suite workflow

The integration tests have recently become a bit flaky in that
individual tests can seem to hang forever. This needs further
investigation. In the meantime we should limit the total allowed time
for the test workflow to something reasonably low. The default timeout
is a very high 360min.

.github/workflows/build.yml

@@ -45,6 +45,7 @@ jobs:
     name: Test Suite
     runs-on: ${{ matrix.os }}
     if: github.repository == 'helix-editor/helix' || github.event_name != 'schedule'
+    timeout-minutes: 30
     env:
       RUST_BACKTRACE: 1
       HELIX_LOG_LEVEL: info