♻️ Refactor date picker header to use semantic <h2> element

[balajis-qb]

Description

Linked issue: #4703

This PR updates the date picker header from a <div> to a semantic <h2> element for improved accessibility.

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 97.23%. Comparing base (66ecc33) to head (8809079).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4712 +/- ## ======================================= Coverage 97.23% 97.23% ======================================= Files 22 22 Lines 2132 2132 Branches 914 901 -13 ======================================= Hits 2073 2073 Misses 59 59 ```

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