x/build/cmd/watchflakes, cmd/go: flaky test timeout

[gopherbot]

#!watchflakes
post <- pkg == "cmd/go" && test == "" && `panic: test timed out`

Bug automatically created to track these flakes.

— watchflakes

[gopherbot]

Found new matching flaky dashboard failures for:

#!watchflakes
post <- pkg == "cmd/go" && test == "" && `panic: test timed out`

2022-09-19 13:56 linux-amd64-longtest go@fc1cddcf cmd/go (log)

go test proxy running at GOPROXY=http://127.0.0.1:43059/mod
panic: test timed out after 45m0s

goroutine 22876 [running]:
panic({0xa58540, 0xc00074a000})
	/workdir/go/src/runtime/panic.go:987 +0x3bb fp=0xc000305f98 sp=0xc000305ed8 pc=0x437d7b
testing.(*M).startAlarm.func1()
	/workdir/go/src/testing/testing.go:2083 +0x8e fp=0xc000305fe0 sp=0xc000305f98 pc=0x529dae
runtime.goexit()
	/workdir/go/src/runtime/asm_amd64.s:1594 +0x1 fp=0xc000305fe8 sp=0xc000305fe0 pc=0x46d601
created by time.goFunc
	/workdir/go/src/time/sleep.go:176 +0x32

— watchflakes

[bcmills]

Duplicate of #50187

[rsc]

Reopened to track my deduplicating.