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

src/test/perl/Makefile

@@ -24,6 +24,7 @@ install: all installdirs
 	$(INSTALL_DATA) $(srcdir)/RecursiveCopy.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/RecursiveCopy.pm'
 	$(INSTALL_DATA) $(srcdir)/PostgresNode.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgresNode.pm'
 	$(INSTALL_DATA) $(srcdir)/PostgreSQL/Test/Cluster.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Cluster.pm'
+	$(INSTALL_DATA) $(srcdir)/PostgreSQL/Test/BackgroundPsql.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/BackgroundPsql.pm'
 	$(INSTALL_DATA) $(srcdir)/PostgreSQL/Test/Utils.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Utils.pm'
 
 uninstall:
@@ -32,6 +33,7 @@ uninstall:
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/RecursiveCopy.pm'
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgresNode.pm'
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Cluster.pm'
+	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/BackgroundPsql.pm'
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Utils.pm'
 
 endif