Run thread sanitizer on 5.1 test CI jobs
Motivation:
Now that SwiftPM with 5.1 supports Linux thread sanitizers, we should run this as part of the normal test pass to catch threading issues.
Modifications:
Add --sanitize=thread
argument to swift test
commands for any job that runs Swift >=5.1.
Result:
More bugs should be caught as soon as possible now that thread races are being monitored.