BUG #16161: pg_ctl stop fails sometimes (on Windows)

The following bug has been logged on the website:

Bug reference:      16161
Logged by:          Alexander Lakhin
Email address:      exclusion@gmail.com
PostgreSQL version: 12.1
Operating system:   Windows
Description:

The regression tests on Windows sometimes fail with 'Permission denied'
errors. For example:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=dory&dt=2019-12-11%2007%3A45%3A33

============== shutting down postmaster               ==============
pg_ctl: could not open PID file
"c:/pgbuildfarm/pgbuildroot/HEAD/pgsql.build/src/test/regress/./tmp_check/data/postmaster.pid":
Permission denied

This error occurs when pg_ctl is trying to open postmaster.pid while this
file is in "delete pending" state
(https://stackoverflow.com/questions/3764072/).