It seems that something broke the Wikibase phpunit tests on the wmf-21 branch. See https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/648283
https://integration.wikimedia.org/ci/job/quibble-vendor-mysql-php72-noselenium-docker/53249/console
```
10:16:36 There was 1 error:
10:16:36
10:16:36 1) Wikibase\Repo\Tests\Hooks\HtmlPageLinkRendererEndHookHandlerTest::testDoHtmlPageLinkRendererBegin_itemIsRedirected
10:16:36 Undefined index: href
10:16:36
10:16:36 /workspace/src/extensions/Wikibase/repo/tests/phpunit/includes/Hooks/HtmlPageLinkRendererEndHookHandlerTest.php:212
10:16:36 /workspace/src/tests/phpunit/MediaWikiIntegrationTestCase.php:437
10:16:36 /workspace/src/maintenance/doMaintenance.php:106
10:16:36 === Logs generated by test case
10:16:36 [objectcache] [debug] MainWANObjectCache using store {class} {"class":"EmptyBagOStuff"}
10:16:36 ===
10:16:36
10:16:36 --
10:16:36
10:16:36 There were 13 failures:
10:16:36
10:16:36 1) Wikibase\Repo\Tests\Hooks\HtmlPageLinkRendererEndHookHandlerTest::testDoHtmlPageLinkRendererBegin_validContext with data set "Special page" (RequestContext Object (...))
10:16:36 Failed asserting that 'Q1' is an instance of class "HtmlArmor".
10:16:36
10:16:36 /workspace/src/extensions/Wikibase/repo/tests/phpunit/includes/Hooks/HtmlPageLinkRendererEndHookHandlerTest.php:43
10:16:36 /workspace/src/tests/phpunit/MediaWikiIntegrationTestCase.php:437
10:16:36 /workspace/src/maintenance/doMaintenance.php:106
10:16:36 === Logs generated by test case
10:16:36 [objectcache] [debug] MainWANObjectCache using store {class} {"class":"EmptyBagOStuff"}
10:16:36 ===
// the other errors are also HtmlPageLinkRendererEndHookHandlerTest
```
This makes back-porting fixes harder and so it would be great if we could figure out what is going on and fix it