chore: update commit button name and add navigation instructions

[BananaApache]

Summary

This PR updates the exercise instructions in Step 4 of review-pull-request exercise to align with the current GitHub UI as of February 2026. The instructions before referenced buttons that might have been outdated, which could lead to user confusion during the "Suggest changes" exercise.

Changes

• Changed references from Add a single comment to the current Comment button.
• Added a step to navigate back to the Conversation tab to find the Commit suggestion button.

Closes: #116

Task list

• For workflow changes, I have verified the Actions workflows function as expected.
• For content changes, I have reviewed the style guide.

[Copilot]

Pull request overview

Updates the Step 4 exercise instructions to match current GitHub PR review UI labels and navigation, reducing confusion during the “Suggest changes” workflow.

Changes:

• Updates the inline comment submission button name to Comment.
• Adds an explicit step to navigate back to the Conversation tab before committing a suggestion.

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[BananaApache]

Updated another button discrepancy (changing Commit changes to Commit suggestion) found by copilot.