os/exec: TestClosePipeOnCopyError failure with `got stuck writing to bad writer` on `solaris-amd64-oraclerel`

[bcmills]

--- FAIL: TestClosePipeOnCopyError (5.01s)
    exec_test.go:964: yes got stuck writing to bad writer
FAIL
FAIL	os/exec	18.215s

greplogs -l -e 'FAIL: TestClosePipeOnCopyError'
2022-05-09T12:02:02-7ca1e2a/solaris-amd64-oraclerel

This test currently has a hard-coded timeout, which I will remove — if the test actually gets stuck, we'll need a goroutine dump to debug it anyway.

[gopherbot]

Change https://go.dev/cl/405434 mentions this issue: os/exec: eliminate some arbitrary short timeouts