Fix typo in GC_collect_or_expand comment

* alloc.c (GC_collect_or_expand): Fix a typo in comment ("setting").

alloc.c

@@ -1237,7 +1237,7 @@ static word last_bytes_finalized = 0;
 
 /* Collect or expand heap in an attempt make the indicated number of    */
 /* free blocks available.  Should be called until the blocks are        */
-/* available (seting retry value to TRUE unless this is the first call  */
+/* available (setting retry value to TRUE unless this is the first call */
 /* in a loop) or until it fails by returning FALSE.                     */
 GC_INNER GC_bool GC_collect_or_expand(word needed_blocks,
                                       GC_bool ignore_off_page,