$filename undefined in UpdateDBCommands.php

[camslice]

Describe the bug
The $filename variable in UpdateDBCommands.php is undefined:

vendor/drush/drush/src/Commands/core/UpdateDBCommands.php:305

To Reproduce
I discovered this bug here: https://www.drupal.org/project/linktitle/issues/3414898

1. Install linktitle module latest version 1.0@beta
2. Update to Drush latest version 12.4.3
3. Run drush updb

Expected behavior
Drush should populate $filename variable and in turn, be able to locate the file containing the post update warning.

Actual behavior
Console output:

[warning] Undefined variable $filename UpdateDBCommands.php:305
[warning] Post update function linktitle_post_update_warning not found in file .php
[error]  Update failed: linktitle_post_update_warning

Workaround
Diff:

diff --git a/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php b/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php
index 7b95deca1..7a724ca11 100644
--- a/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php
+++ b/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php
@@ -263,6 +263,7 @@ public static function updateDoOnePostUpdate(string $function, array $context):
         }
 
         list($extension, $name) = explode('_post_update_', $function, 2);
+        $filename = $extension . '.post_update';
         $update_registry = \Drupal::service('update.post_update_registry');
         // https://www.drupal.org/project/drupal/issues/3259188 Support theme's
         // having post update functions when it is supported in Drupal core.

System Configuration

Q	A
Drush version?	12.14.3
Drupal version?	10.2.1
PHP version	8.1.18
OS?	macOS 10.15.7