add 'week' and 'weeks' to Arabic locale

[AbdullahAlajmi]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• [ x ] 🧪 Added tests for changed code.
• [ x ] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [ x ] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [ x ] 📚 Updated documentation for changed code.
• [ x ] ⏩ Code is up-to-date with the master branch.

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

• Added 'week' and 'weeks' to Arabic Locale.
• Added tests to new changes.

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (de0aea9) 100.00% compared to head (9ca0b86) 100.00%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1155 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 10 10 Lines 2326 2326 Branches 400 400 ========================================= Hits 2326 2326 ``` | [Files](https://app.codecov.io/gh/arrow-py/arrow/pull/1155?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arrow-py) | Coverage Δ | | |---|---|---| | [arrow/locales.py](https://app.codecov.io/gh/arrow-py/arrow/pull/1155?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arrow-py#diff-YXJyb3cvbG9jYWxlcy5weQ==) | `100.00% <ø> (ø)` | |

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