Run tests sequentially in CI

The parallel test logs are just so hard to read that they don’t really provide any value. Locally, running the tests in serial only increases test times by 1 minute, which I think is a tradeoff worth making to actually be able to tell what’s going wrong in CI.

Author: ahoppen

Utilities/build-script-helper.py

@@ -210,7 +210,6 @@ def run_tests(swift_exec: str, args: argparse.Namespace) -> None:
 
     cmd = [
         swift_exec, 'test',
-        '--parallel',
         '--disable-testable-imports',
         '--test-product', 'SourceKitLSPPackageTests'
     ] + swiftpm_args