Fix check_marttra function to handle 'กร' as a final consonant correctly

Fixes #966

Fixes the `check_marttra` function to handle "กร" as a final consonant correctly.

* Modifies the `check_marttra` function in `pythainlp/khavee/core.py` to return "กก" for words ending with "กร".
* Updates the test case for `check_marttra("จักร")` in `tests/core/test_khavee.py` to expect "กก".
* Resolves the issue affecting other test cases in `tests/core/test_khavee.py` such as "ขำ", "รมย์", "ทัย", "ไทย", "ไกล", "ใกล้", "โยชน์", "ยนต์", and "กรรณ".

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/PyThaiNLP/pythainlp/issues/966?shareId=XXXX-XXXX-XXXX-XXXX).

Author: wannaphong