tsl/test: pass PG_PKGLIBDIR to provecheck-t's pg_prove.sh invocation

provecheck-t's custom target never set PG_PKGLIBDIR in the
environment it invokes pg_prove.sh with, unlike the community
provecheck target (test/CMakeLists.txt), which does.

pg_prove.sh builds its Perl -I include path from PG_PKGLIBDIR to find
PostgreSQL::Test::Cluster:

    -I "${PG_PKGLIBDIR}/pgxs/src/test/perl"

With PG_PKGLIBDIR unset, every TSL TAP test fails immediately with
"Can't locate PostgreSQL/Test/Cluster.pm in @inc", on any system where
that module isn't also reachable via PG_LIBDIR's own search path
(e.g. Debian/Ubuntu PGDG packages, where pg_config --pkglibdir and
--libdir point at different directories).

Author: tureba

tsl/test/CMakeLists.txt

@@ -82,7 +82,8 @@ if(TAP_CHECKS)
       CONFDIR=${CMAKE_BINARY_DIR}/tsl/test PATH="${PG_BINDIR}:$ENV{PATH}"
       PG_REGRESS=${PG_REGRESS} SRC_DIR=${PG_SOURCE_DIR}
       CM_SRC_DIR=${CMAKE_SOURCE_DIR} PG_LIBDIR=${PG_LIBDIR}
-      PG_VERSION_MAJOR=${PG_VERSION_MAJOR} ${PRIMARY_TEST_DIR}/pg_prove.sh
+      PG_PKGLIBDIR=${PG_PKGLIBDIR} PG_VERSION_MAJOR=${PG_VERSION_MAJOR}
+      ${PRIMARY_TEST_DIR}/pg_prove.sh
     USES_TERMINAL)
   list(APPEND _install_checks provecheck-t)
 elseif(REQUIRE_ALL_TESTS)