pgsql: Skip TAP test for peer authentication if there are no unix-domai

Skip TAP test for peer authentication if there are no unix-domain sockets

Peer connections require support for local connections to work, but the
test missed the same check as the other ones in this suite.  The
buildfarm does not run the authentication tests on Windows, and, more
surprisingly, the CI with meson was already able to skip it.

Author: Anton A. Melnikov
Discussion: https://postgr.es/m/28b9d685-9590-45b1-fe87-358d61c6950a@inbox.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9e492d6b693a60d53a5d3d8fbd40ae253b7d22f5

Modified Files
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src/test/authentication/t/003_peer.pl | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)