Docs (tooltips): Fix "them" typo in markup section

[EricDunsworth]

Description

Renames "theme" to "them" in the tooltip documentation's markup callout.

• Before:

  Additionally, do not rely solely on hover as the trigger for your tooltips as this will make theme impossible to trigger for keyboard users.

• After:

  Additionally, do not rely solely on hover as the trigger for your tooltips as this will make them impossible to trigger for keyboard users.

Motivation & Context

Makes the documentation more readable.

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-38751--twbs-bootstrap.netlify.app/
  • https://deploy-preview-38751--twbs-bootstrap.netlify.app/docs/5.3/components/tooltips/#markup

[julien-deramond]

Thanks @EricDunsworth