Fix a PHP 8.1 string strictness issue in repositories

Summary: Ref T13588. This is a little too strict, as `$line` may be an integer.

Test Plan: Will deploy

Maniphest Tasks: T13588

Differential Revision: https://secure.phabricator.com/D21775

src/applications/repository/storage/PhabricatorRepository.php

@@ -757,6 +757,7 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO
       $commit = ';'.phutil_escape_uri($commit);
     }
 
+    $line = phutil_string_cast($line);
     if (phutil_nonempty_string($line)) {
       $line = '$'.phutil_escape_uri($line);
     }