Fix TailCursorDoctrineODMCommand Static Analysis

[mustanggb]

Fix the following complaints from Static Analysis.

[InvalidNullableReturnType: Command/TailCursorDoctrineODMCommand.php#L111](https://github.com/mustanggb/DoctrineMongoDBBundle/commit/294b0fb99432bd5a21dbcc24f87f195bcb2cf7b8#annotation_15142273754)
Command/TailCursorDoctrineODMCommand.php:111:17: InvalidNullableReturnType: The declared return type 'Psr\Container\ContainerInterface' for Doctrine\Bundle\MongoDBBundle\Command\TailCursorDoctrineODMCommand::getContainer is not nullable, but 'Symfony\Component\DependencyInjection\ContainerInterface|null' contains null (see https://psalm.dev/144)

[NullableReturnStatement: Command/TailCursorDoctrineODMCommand.php#L114](https://github.com/mustanggb/DoctrineMongoDBBundle/commit/294b0fb99432bd5a21dbcc24f87f195bcb2cf7b8#annotation_15142273760)
Command/TailCursorDoctrineODMCommand.php:114:16: NullableReturnStatement: The declared return type 'Psr\Container\ContainerInterface' for Doctrine\Bundle\MongoDBBundle\Command\TailCursorDoctrineODMCommand::getContainer is not nullable, but the function returns 'Symfony\Component\DependencyInjection\ContainerInterface|null' (see https://psalm.dev/139)

[mustanggb]

Duplicate of #780.