Psalm: suppress notice about preg_split $flags

As discussed in the PR:
> > Argument 4 of preg_split expects 0|1|2|3|4|5|6|7, parent type int provided (see https://psalm.dev/193)
>
> I believe this issue is for the `phpDocumentor\Reflection\Utils` class and expects the `pregSplit()` method to apply input validation to the value received for `$flags` before passing it off to the PHP native `preg_split()` function.
>
> IMO that's taking things a little too far as PHP will handle this internally without errors.
> See: https://3v4l.org/NdDRK

psalm.xml

@@ -53,5 +53,12 @@
                 <file name="src/Utils.php"/>
             </errorLevel>
         </InvalidReturnStatement>
+
+        <ArgumentTypeCoercion>
+            <errorLevel type="info">
+                <!-- PHP handles invalid preg_split flags just fine. -->
+                <file name="src/Utils.php"/>
+            </errorLevel>
+        </ArgumentTypeCoercion>
     </issueHandlers>
 </psalm>