[Docs] Update page for the Testimonial component to correct spelling and grammar

[iannl]

Summary

Fixed grammar and spelling mistakes in Testimonial component doc page.

List of notable changes:

• updated page to fix grammar and spelling mistakes
• updated page to make wording less verbose (customers' sentiments -> customer sentiment)

What should reviewers focus on?

N/A

Steps to test:

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Supporting resources (related issues, external links, etc):

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Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

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Latest commit: 9016019

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[rezrah]

Thanks for these updates @iannl!