Add change log entry for ^^ operator handling changes

[xoxorwr]

People keep forgetting to including a change log entry, this is annoying to track.

There should be a CI gate to block any PR modifying druntime that does not include a corresponding changelog entry.

#22831

#22835

[dlang-bot]

Thanks for your pull request and interest in making D better, @xoxorwr! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#22838"

[ibuclaw]

It was never expanded inline by the compiler. Previously it was forwarding to std.math in phobos.

[xoxorwr]

Another reason to enforce change log entries to be written with the PR by its author, I remembered wrong, I should have checked the diff properly.

[dkorpel]

I was going to add one, but I'm still working on this but was away on Sunday so I didn't respond immediately. Thanks for adding one in the mean time though!