pgsql: Fix missing installation/uninstallation rules for BackgroundPsql

Fix missing installation/uninstallation rules for BackgroundPsql.pm

Commit d5fd7865 backported BackgroundPsql perl module module with
helper functions for tests running interactive or background psql
tasks to PG 12 to 15, but did not add installation/uninstallation
rules of the build system, causing problems running TAP tests for the
extensions.

Author: Pavan Deolasee <pavan.deolasee@gmail.com>
Discussion:
https://www.postgresql.org/message-id/CABOikdPmRuZrcf_gtgXmQzZ5Tbg9yUJmqXDCAZ2aW%3DWi-PbDyQ%40mail.gmail.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/241ef53b6a95be0c7c175cbad48e5492dc3ae29c

Modified Files
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src/test/perl/Makefile | 2 ++
1 file changed, 2 insertions(+)