fix calendar weekday name with custom styles

[atarek12]

Description

Linked issue: #(issue number)

Problem
There is an issue with weekday name when using datepicker component without using datepicker styles
i.e: import "react-datepicker/dist/react-datepicker.css";

Changes
The issue has been introduced in this pr that fixes this issue.
But instead of using sr-only class on an extra span element which will be rendered if we don't import the stylesheet.
I have reverted it back to use aria-label but kept the inner span with aria-hidden="true"; so the screen-readers will skip it and announce the aria-label prop.

Screenshots

• Before: Notice the duplicate of weekday -> SundaySu

• After

Contribution checklist

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

[martijnrusschen]

Please check the output of the failing CI

[martijnrusschen]

Looks like there's a failing test here. Please resolve that.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.21%. Comparing base (1122aba) to head (c7e4e3d).
⚠️ Report is 69 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5988      +/-   ##
==========================================
+ Coverage   98.91%   99.21%   +0.30%     
==========================================
  Files          30       30              
  Lines        3496     3579      +83     
  Branches     1470     1529      +59     
==========================================
+ Hits         3458     3551      +93     
+ Misses         37       27      -10     
  Partials        1        1              

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[martijnrusschen]

Thank you for your PR! Unfortunately, we can't merge this change.

The aria-label approach breaks axe accessibility tests with "empty-table-header" violations. When columnheader elements only contain , screen readers have no text to announce.

The existing sr-only span pattern is the correct accessibility approach - it provides visible text for screen readers while hiding it visually. This pattern requires the CSS stylesheet to be imported, which is already expected for the component to function properly (layout, colors, positioning, etc.).

If you're using the datepicker without importing the stylesheet, we'd recommend importing it or providing your own styles that include the .react-datepicker__sr-only class definition.