cmd/go: exec: WaitDelay expired before I/O complete

[prattmic]

#!watchflakes
post <- `^exec: WaitDelay expired before I/O complete`

I only see one prior failure (posted to #56785):

2023-01-24T19:47:54-ffbd194/freebsd-arm-paulzhol

This seems to be a case of the test passing, but slow scheduling preventing Wait in the parent from returning quickly enough.

[bcmills]

Looks like we need to adjust the WaitDelay heuristic following CL 456116 (#24050).

[gopherbot]

Change https://go.dev/cl/464555 mentions this issue: cmd/go/internal/test: scale the WaitDelay for test subprocesses