Fix: [Accessibility] [Global] [Datagrid] Selectable and Sortable> 'Sort Rows' button is unnecessarily marked-up as column header

[moathabuhamad-cengage]

Closes: #1946

What I did

Fixed semantic markup for Sort Rows button in selectable and sortable variant. The button now uses a <td> element instead of <th>, preventing screen readers from incorrectly announcing it as a column header for checkbox cells.

Screenshots

Checklist

• [x] changeset has been added
• [x] Pull request is assigned, labels have been added and ticket is linked
• [x] Pull request description is descriptive and testing steps are listed
• [x] Corresponding changes to the documentation have been made
• [x] New and existing unit tests pass locally with the proposed changes
• [x] Tests that prove the fix is effective or that the feature works have been added

How to test

got to storybook Datagrid--selectable-and-sortable test screen reader output