bump: use semicolon skip messages delimiter

[samford]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

---

• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes.

---

We recently updated Livecheck::SkipConditions.print_skip_information to join messages using a semicolon, so this updates the similar logic in brew bump to use the same delimiter.

This is a follow-up to #21708, where I requested this change in review.

[Copilot]

Pull request overview

This PR tweaks brew bump’s livecheck skip-status output formatting to use a semicolon-separated list when multiple skip messages are present, aligning it with existing livecheck skip messaging conventions.

Changes:

• Change livecheck skip message joining from ", " to "; " in Homebrew::DevCmd::Bump#livecheck_result.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.