Disable regex tests when repl feature not enabled

[notmandatory]

Description

I noticed that when I disable default features and don't enable the repl feature that the regex tests fail because they need the regex dependency that the repl feature brings in. This PR is to simply disable the regex related test code if the repl feature isn't enabled.

Notes to the reviewers

Checklists

All Submissions:

• [x] I've signed all my commits
• [x] I followed the contribution guidelines
• [x] I ran cargo fmt and cargo clippy before committing

New Features:

• [ ] I've added tests for the new feature
• [ ] I've added docs for the new feature
• [ ] I've updated CHANGELOG.md

Bugfixes:

• [ ] This pull request breaks the existing API
• [ ] I've added tests to reproduce the issue which are now passing
• [ ] I'm linking the issue being fixed by this PR