Post-merge builds often fail (at least in #growthexperiments but I doubt it's extension-specific) with `Command 'mwext-phpunit-coverage' returned non-zero exit status 1.` E.g. https://integration.wikimedia.org/ci/job/mwext-phpunit-coverage-docker-publish/37063/console for https://gerrit.wikimedia.org/r/c/mediawiki/extensions/GrowthExperiments/+/675330.
Probably because of this:
```
PHP Warning: Failed loading Zend extension 'xdebug.so' (tried: /usr/lib/php/20180731/xdebug.so (/usr/lib/php/20180731/xdebug.so: cannot open shared object file: No such file or directory), /usr/lib/php/20180731/xdebug.so.so (/usr/lib/php/20180731/xdebug.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
17:19:12 Using PHP 7.3.27-9+0~20210227.82+debian10~1.gbpa4a3d6
```