Fix test expectation for PHP 8.0

Since float to string conversion is no longer locale dependent, we have
to expect a dot as decimal separator.

ext/mysqli/tests/bug74779.phpt

@@ -38,5 +38,5 @@ mysqli_close($link);
 --EXPECT--
 array(1) {
   ["ST_Y(Point(56.7, 53.34))"]=>
-  float(53,34)
+  float(53.34)
 }