message: CI: Temporarily run tests with only one thread
  Until we have proper synchronization for test fixtures.
diff: @@ -7,7 +7,9 @@ matrix:
  # tests pass
  - rust: nightly
  script:
  - - cargo test --locked
  + # XXX: `--test-threads 1` is a hack until we have a proper fix for
  + # synchronizing access to the fixtures.
  + - cargo test --locked -- --test-threads 1
  - rustup component add rustfmt-preview
  - cargo fmt --all -- --check
  env: RUST_BACKTRACE=1
  