testing: data race on done between Run() and Log()

[fraenkel]

Using 1.15.2

WARNING: DATA RACE
Read at 0x00c0002dedc3 by goroutine 25
  testing.(*common).logDepth()
      /usr/local/go/src/testing/testing.go:736 +0xa9
  testing.(*common).log()
      /usr/local/go/src/testing/testing.go:729 +0x8f
  testing.(*common).Logf()
      /usr/local/go/src/testing/testing.go:775 +0x21
  testing.(*T).Logf()

Previous write at 0x00c0002dedc3 by goroutine 20
  testing.tRunner.func1()
      /usr/local/go/src/testing/testing.go:1113 +0x484
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1131 +0x22a

Just looks like we are missing a lock/unlock pair.

[ALTree]

Please post a code sample that triggers the problem.

[fraenkel]

dupe of #40343