PHP 8.1 require to declare a return type. When not doing so, the notice is printed.
A simple workaround might be using the `#[\ReturnTypeWillChange]` attribute to suppress the error message; cf rARC3626582354e4fc62191927a80b274ec71284cb77.
Output from PHPStan:
* https://we.phorge.it/source/phorge/browse/master/src/applications/fact/extract/PhabricatorFactUpdateIterator.php$36
** Return type mixed of method `PhabricatorFactUpdateIterator::key()` is not covariant with tentative return type mixed of method `Iterator::key()`. Make it covariant, or use the `#[\ReturnTypeWillChange]` attribute to temporarily suppress the error.
* https://we.phorge.it/source/phorge/browse/master/src/applications/harbormaster/storage/build/HarbormasterBuildLogChunkIterator.php$21
** Return type mixed of method `HarbormasterBuildLogChunkIterator::key()` is not covariant with tentative return type mixed of method `Iterator::key()`. Make it covariant, or use the `#[\ReturnTypeWillChange]` attribute to temporarily suppress the error.
* https://we.phorge.it/source/phorge/browse/master/src/infrastructure/storage/lisk/LiskMigrationIterator.php$29
** Return type mixed of method `LiskMigrationIterator::key()` is not covariant with tentative return type mixed of method `Iterator::key()`. Make it covariant, or use the `#[\ReturnTypeWillChange]` attribute to temporarily suppress the error.
* https://we.phorge.it/source/phorge/browse/master/src/infrastructure/storage/lisk/LiskRawMigrationIterator.php$19
** Return type mixed of method `LiskRawMigrationIterator::key()` is not covariant with tentative return type mixed of method `Iterator::key()`. Make it covariant, or use the `#[\ReturnTypeWillChange]` attribute to temporarily suppress the error.
* https://we.phorge.it/source/phorge/browse/master/src/infrastructure/storage/lisk/PhabricatorQueryIterator.php$21
** Return type mixed of method `PhabricatorQueryIterator::key()` is not covariant with tentative return type mixed of method `Iterator::key()`. Make it covariant, or use the `#[\ReturnTypeWillChange]` attribute to temporarily suppress the error.