fix(complex-numbers): use runner's Catch2 version

[ahans]

The test runner uses Catch2 v3.4.0, while locally we still had v2.13.6. The recent changes to the complex-numbers test work with v2.13.6, while they don't work with v3.4.0, causing compilation to always fail in the test runner. This commit changes the test to be compatible with v3.4.0 and updates the local Catch2 copy.

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[ahans]

@vaeng This should fix the issue introduced with #995. I also tested locally with the test runner. Things are working now.

[vaeng]

Thanks for taking your time fixing this

[ahans]

I also created #997 and #998 so we don't forget about follow-ups.