Update .php handling to keep <?php at the top

Looking at https://www.php.net/manual/en/language.basic-syntax.phptags.php
there are just too many variations and I'm not convinced the added
complexity to support all of them would be worth it here.

Thus, support only the case where closing tag "?>" is either omitted
or on a separate line. A workaround for all other cases is to add
the license header manually.

Can always revisit this later.

testdata/initial/file.php

@@ -1 +1,3 @@
-<?php phpinfo(); ?>
+<?php
+namespace App;
+phpinfo();