Search: Fix modal on mobile chromium based browsers

[louismaximepiton]

Description

Set the position to have always the same.

Motivation & Context

Some issue on mobile breakpoint when using Chrome or Chromium based with search modal from Algolia.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-39739--twbs-bootstrap.netlify.app/

Related issues

Fixes #39665.

[julien-deramond]

LGTM! The position: fixed doesn't seem to imply some visual regressions and it fixes the issue that was reproducible on basically all browsers on my side.