Fixed return type for CriteriaInterface::getLimit

[sergeyklay]

Hello!

• Type: bug fix
• Link to issue: [BUG]: Incorrect return type hint of Phalcon\Mvc\Model\CriteriaInterface::getLimit() #15004

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Small description of change:

• Changed return type for Phalcon\Mvc\Model\Criteria::getLimit so that integer, NULL or array will be returned
• Fixed return type hint for Phalcon\Mvc\Model\CriteriaInterface::getLimit and Phalcon\Mvc\Model\Criteria::getLimit to follow documentation and original purpose
  Thanks

[niden]

LGTM