pgsql: Fix recovery test hang in 021_row_visibility.pl on windows.

Fix recovery test hang in 021_row_visibility.pl on windows.

The psql processes were not explicitly killed (but would eventually
exit due postgres shutting down). For some reason windows perl doesn't
like that, resulting in errors like
Warning: unable to close filehandle GEN20 properly: Bad file descriptor during global destruction.

The test was introduced in d6734a897e3, so no backpatching necessary.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/1e6e40447115ca7b4749d7d117b81b016ee5e2c2

Modified Files
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src/test/recovery/t/021_row_visibility.pl | 4 ++++
1 file changed, 4 insertions(+)