Since we updated to PHPStan 0.12.83 we started getting the error bellow.
It seems this happened because the message of an error that we were
already ignoring was changed. This commit simply updates the pattern we
use to ignore the error to reflect the change in the new PHPStan
version.
```
------ ---------------------------------------------------------------------
Line lib/Features/FeatureFlagsController.php
------ ---------------------------------------------------------------------
Ignored error pattern #^Cannot access offset \(int\|string\) on
array\|false# in path
/home/circleci/mailpoet/lib/Features/FeatureFlagsController.php was
not matched in reported errors.
44 Cannot access offset (int|string) on array<string,
MailPoet\Entities\FeatureFlagEntity>|false.
------ ---------------------------------------------------------------------
```
[MAILPOET-3491]
