`log_vc_info`: add tests for when VCS not installed

[MetRonnie]

Just adding some tests after doing the same in https://github.com/metomi/rose/pull/2818

Check List

• [x] I have read CONTRIBUTING.md and added my name as a Code Contributor.
• [x] Contains logically grouped changes (else tidy your branch by rebase).
• [x] Does not contain off-topic changes (use other PRs for other changes).

[MetRonnie]

(Current test failure is unrelated - flaky Tui integration tests)