PGPRO-13772, PGPRO-15606: temporarily disable the corner_cases test

This commit must be reverted later.

Author: Marina Polyakova

Makefile

@@ -13,7 +13,6 @@ PGFILEDESC = "pg_query_state - facility to track progress of plan execution"
 EXTRA_CLEAN = ./isolation_output $(EXTENSION)--$(EXTVERSION).sql \
 	Dockerfile ./tests/*.pyc ./tmp_stress
 
-ISOLATION = corner_cases
 ISOLATION_OPTS = --load-extension=pg_query_state
 
 TAP_TESTS = 1