go: runtime/pprof: TestCPUProfileWithFork failures with stuck `writerDescriptor` goroutines

#!watchflakes
post <- goos == "darwin" && pkg == "runtime/pprof" && test == "TestCPUProfileWithFork" && `SIGQUIT: quit`

Issue created automatically to collect these failures.

Example (log):

SIGQUIT: quit
PC=0x7ff8061563ea m=1 sigcode=0

rax    0x104
rbx    0x70000a473000
rcx    0x70000a472c48
rdx    0x1a00
rdi    0xc000040380
rsi    0xa1c01000a1d00
rbp    0x70000a472cf0
...
	/tmp/buildlet/go/src/runtime/chan.go:107 +0xe5 fp=0xc0000b9a88 sp=0xc0000b9a48 pc=0x1055c85
os/exec.(*Cmd).Start(0xc00013e000)
	/tmp/buildlet/go/src/os/exec/exec.go:706 +0xa0f fp=0xc0000b9ce0 sp=0xc0000b9a88 pc=0x117696f
os/exec.(*Cmd).Run(0x0?)
	/tmp/buildlet/go/src/os/exec/exec.go:587 +0x27 fp=0xc0000b9d20 sp=0xc0000b9ce0 pc=0x1175ee7
os/exec.(*Cmd).CombinedOutput(0xc00013e000)
	/tmp/buildlet/go/src/os/exec/exec.go:1005 +0x1f7 fp=0xc0000b9d98 sp=0xc0000b9d20 pc=0x1178df7
runtime/pprof.TestCPUProfileWithFork(0xc000082820)
	/tmp/buildlet/go/src/runtime/pprof/pprof_test.go:687 +0x338 fp=0xc0000b9e98 sp=0xc0000b9d98 pc=0x12339b8
testing.tRunner(0xc000082820, 0x12b3970)

— watchflakes