Use PG_TEST_SKIP="...aqo..." to skip aqo tests if necessary

Makefile

@@ -8,6 +8,8 @@ OBJS = aqo.o auto_tuning.o cardinality_estimation.o cardinality_hooks.o \
 hash.o machine_learning.o path_utils.o postprocessing.o preprocessing.o \
 selectivity_cache.o storage.o utils.o ignorance.o $(WIN32RES)
 
+# Use PG_TEST_SKIP="...aqo..." to skip aqo tests if necessary.
+ifneq (aqo,$(filter aqo,$(PG_TEST_SKIP)))
 TAP_TESTS = 1
 
 REGRESS =	aqo_disabled \
@@ -19,6 +21,7 @@ REGRESS =	aqo_disabled \
 			aqo_fdw \
 			aqo_CVE-2020-14350 \
 			gucs
+endif
 
 fdw_srcdir = $(top_srcdir)/contrib/postgres_fdw
 PG_CPPFLAGS += -I$(libpq_srcdir) -I$(fdw_srcdir)