Ensure all perl test modules are installed

PostgreSQL::Test::Cluster and ::Utils were not being installed.  This is
very hard to notice, as it only seems to affect external modules that
want to run tests from 15 back in earlier versions.  Oversight in
b235d41d.

This applies only to branches 14 and back, because 15 had already been
made correct in commit b3b4d8e68ae8.

Discussion: https://postgr.es/m/20221010093415.poplkyn7pjeiv2y7@alvherre.pgsql

src/test/perl/Makefile

@@ -16,7 +16,7 @@ include $(top_builddir)/src/Makefile.global
 ifeq ($(enable_tap_tests),yes)
 
 installdirs:
-	$(MKDIR_P) '$(DESTDIR)$(pgxsdir)/$(subdir)'
+	$(MKDIR_P) '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test'
 
 install: all installdirs
 	$(INSTALL_DATA) $(srcdir)/TestLib.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/TestLib.pm'
@@ -24,6 +24,8 @@ 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) $(srcdir)/PostgresVersion.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgresVersion.pm'
+	$(INSTALL_DATA) $(srcdir)/PostgreSQL/Test/Cluster.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Cluster.pm'
+	$(INSTALL_DATA) $(srcdir)/PostgreSQL/Test/Utils.pm '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Utils.pm'
 
 uninstall:
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/TestLib.pm'
@@ -31,5 +33,7 @@ uninstall:
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/RecursiveCopy.pm'
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgresNode.pm'
 	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgresVersion.pm'
+	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Cluster.pm'
+	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/PostgreSQL/Test/Utils.pm'
 
 endif