Fix branch prediction in Ensure

PR #6648 introduces a branch prediction in the Ensure macro. However,
the checked condition needs to be negated to be unlikely. Therefore, the
check predicts the branch likelihood wrongly. In other words, reporting
an error in Ensure should be the unlikely case, and the condition should
be fulfilled in most calls. This commit fixes the branch prediction.

src/debug_assert.h

@@ -29,7 +29,7 @@
 #define Ensure(COND, FMT, ...)                                                                     \
 	do                                                                                             \
 	{                                                                                              \
-		if (!unlikely(COND))                                                                       \
+		if (unlikely(!(COND)))                                                                     \
 			ereport(ERROR,                                                                         \
 					(errcode(ERRCODE_INTERNAL_ERROR),                                              \
 					 errdetail("Assertion '" #COND "' failed."),                                   \