Fix unit tests

Regression caused by https://github.com/owncloud/core/pull/16721

Failed the unit tests as per https://ci.owncloud.org/job/server-master-linux/database=sqlite,label=SLAVE/1994/testReport/junit/(root)/Test_Encryption_ManagerTest/testGetEncryptionModuleUnknown/:
```
Test\Encryption\ManagerTest::testGetEncryptionModuleUnknown
Failed asserting that exception message 'Module with id: unknown does not exist.' contains 'Module with id: unknown does not exists.'
```