Commits backported for MediaWiki core wmf.13, or any other extension, are failing consistently in Jenkins with the following error:
```
[efc43edb347f32d9a3043181] [no req] Wikimedia\Rdbms\DBQueryError from line 1145 of /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/includes/libs/rdbms/database/Database.php: A database query error has occurred. Did you forget to run your application's database schema updater after upgrading?
00:03:29.553 Query: TRUNCATE TABLE `unittest_ip_changes`
00:03:29.553 Function: MediaWikiTestCase::resetDB
00:03:29.554 Error: 1146 Table 'jenkins_u0_mw.unittest_ip_changes' doesn't exist (127.0.0.1:3306)
00:03:29.554
00:03:29.554 Backtrace:
00:03:29.554 #0 /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/includes/libs/rdbms/database/Database.php(975): Wikimedia\Rdbms\Database->reportQueryError(string, integer, string, string, boolean)
00:03:29.554 #1 /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/tests/phpunit/MediaWikiTestCase.php(1323): Wikimedia\Rdbms\Database->query(string, string)
```
I believe this is triggered by unit tests form the Wikidata extension. At first that seems fine (the table was recently added to MediaWiki core master, and Wikidata master uses it).
The problem is that when submitting commits for wmf.13 branches of mediawiki-core or any deployed extension, the build fails because Wikidata does not have a wmf.13 branch, so Zuul falls back to checking out the master branch instead - which then fails because it's using tables that don't exist in core wmf.13.
This is among the reasons all deployed extensions should be branched every week from master so that it contains a saved snapshot that is compatible (even if we maybe don't end up using the branch some weeks).
Please create a wmf.13 branch for Wikidata, so that SWAT and other deployments can continue without needing to bypass Jenkins build failures.