Assert only valid flag bits are passed to visibilitymap_set()

If visibilitymap_set() is called with flags containing a higher bit than
VISIBILITYMAP_ALL_FROZEN, the state of neighboring pages is affected. While
there was an assertion that *some* valid bits were set, it did not check
that *only* valid bits were. Change that.

Discussion: https://postgr.es/m/20230331043300.gux3s5wzrapqi4oe@awork3.anarazel.de

src/backend/access/heap/visibilitymap.c

@@ -259,9 +259,9 @@ visibilitymap_set(Relation rel, BlockNumber heapBlk, Buffer heapBuf,
 
 	Assert(InRecovery || XLogRecPtrIsInvalid(recptr));
 	Assert(InRecovery || PageIsAllVisible((Page) BufferGetPage(heapBuf)));
+	Assert((flags & VISIBILITYMAP_VALID_BITS) == flags);
 
 	/* Must never set all_frozen bit without also setting all_visible bit */
-	Assert(flags & VISIBILITYMAP_VALID_BITS);
 	Assert(flags != VISIBILITYMAP_ALL_FROZEN);
 
 	/* Check that we have the right heap page pinned, if present */