[typescript-migration] src/test/month_year_dropdown_test.test.tsx and month_dropdown_test.test.tsx

[yuki0410-dev]

Description

Linked issue: #4700

Changes

• migrate src/test/month_year_dropdown_test.test.tsx
• migrate src/test/month_dropdown_test.test.tsx

Contribution checklist

• [x] I have followed the contributing guidelines.
• [x] I have added sufficient test coverage for my changes.
• [x] I have formatted my code with Prettier and checked for linting issues with ESLint for code readability.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.96%. Comparing base (1b0a813) to head (894fe39).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4880 +/- ## ======================================= Coverage 96.96% 96.96% ======================================= Files 28 28 Lines 3234 3234 Branches 1337 1337 ======================================= Hits 3136 3136 Misses 94 94 Partials 4 4 ```

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[yuki0410-dev]

I always appreciate your prompt reviews.