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_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9d7506a2f7cb2b040fc78886fb2b2b6d0feb68a1

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