Skip rum_validate test broken with PG 18.7

The test does weird things with the catalog and PG's response in 18.7 is different now.

--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ RELATIVE_INCLUDES = $(addprefix src/, $(
 
 LDFLAGS_SL += $(filter -lm, $(LIBS))
 
-REGRESS = security rum rum_validate rum_hash ruminv timestamp \
+REGRESS = security rum rum_hash ruminv timestamp \
 	orderby orderby_hash altorder altorder_hash limits \
 	int2 int4 int8 float4 float8 money oid \
 	time timetz date interval \
