pgsql: Reference test binary using TESTDIR in 001_libpq_pipeline.pl.

Reference test binary using TESTDIR in 001_libpq_pipeline.pl.

The previous approach didn't really work on windows, due to the PATH separator
being ';' not ':'. Instead of making the PATH change more complicated,
reference the binary using the TESTDIR environment.

Reported-By: Andres Freund <andres@anarazel.de>
Suggested-By: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/20210930214040.odkdd42vknvzifm6@alap3.anarazel.de
Backpatch: 14-, where the test was introduced.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/795862c280c5949bafcd8c44543d887fd32b590a

Modified Files
--------------
src/test/modules/libpq_pipeline/t/001_libpq_pipeline.pl | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)