Fix bad indentation introduced in 43cd30bcd1

Oops.

Reported-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://postgr.es/m/ZpVZB9rH5tHllO75@nathan
Backpatch: 12-, like 43cd30bcd1

src/backend/utils/misc/guc.c

@@ -1289,8 +1289,8 @@ find_option(const char *name, bool create_placeholders, bool skip_errors,
 static int
 guc_var_compare(const void *a, const void *b)
 {
-	const char *namea = **(const char ** const *) a;
-	const char *nameb = **(const char ** const *) b;
+	const char *namea = **(const char **const *) a;
+	const char *nameb = **(const char **const *) b;
 
 	return guc_name_compare(namea, nameb);
 }