net/http: data race in `testServerExpect`

[gopherbot]

#!watchflakes
post <- pkg == "net/http" && log ~ `WARNING: DATA RACE` && log ~ `net/http_test.testServerExpect`

Issue created automatically to collect these failures.

Example (log):

==================
WARNING: DATA RACE
Read at 0x00c0004d81e3 by goroutine 12452:
  testing.(*common).logDepth()
      /workdir/go/src/testing/testing.go:998 +0x4c4
  testing.(*common).log()
      /workdir/go/src/testing/testing.go:985 +0xa4
  testing.(*common).Logf()
      /workdir/go/src/testing/testing.go:1036 +0x6a
  net/http_test.testServerExpect.func2.1()
...
  testing.(*M).Run()
      /workdir/go/src/testing/testing.go:1906 +0xb44
  net/http_test.TestMain()
      /workdir/go/src/net/http/main_test.go:23 +0x2e
  main.main()
      _testmain.go:1119 +0x324
==================
--- FAIL: TestOnlyWriteTimeout (0.00s)
    --- FAIL: TestOnlyWriteTimeout/h1 (0.02s)
        testing.go:1446: race detected during execution of test

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestOnlyWriteTimeout"

2023-07-06 19:41 linux-amd64-race go@312920c0 net/http.TestOnlyWriteTimeout (log)

==================
WARNING: DATA RACE
Read at 0x00c0004d81e3 by goroutine 12452:
  testing.(*common).logDepth()
      /workdir/go/src/testing/testing.go:998 +0x4c4
  testing.(*common).log()
      /workdir/go/src/testing/testing.go:985 +0xa4
  testing.(*common).Logf()
      /workdir/go/src/testing/testing.go:1036 +0x6a
  net/http_test.testServerExpect.func2.1()
...
  testing.(*M).Run()
      /workdir/go/src/testing/testing.go:1906 +0xb44
  net/http_test.TestMain()
      /workdir/go/src/net/http/main_test.go:23 +0x2e
  main.main()
      _testmain.go:1119 +0x324
==================
--- FAIL: TestOnlyWriteTimeout (0.00s)
    --- FAIL: TestOnlyWriteTimeout/h1 (0.02s)
        testing.go:1446: race detected during execution of test

— watchflakes

[bcmills]

(attn @neild)

[bcmills]

Note that commit 312920c is on release-branch.go1.20. It is not obvious to me whether this race also exists on the main branch.

[bcmills]

Duplicate of #59883