Since adding auto-detection of the call site, we've had 2-3 cases where the call site was still being printed wrong.  I happened to notice them.  Here's the background to those times:

* Our original regex was something like `%r{/lib/rspec/(core|mocks|expectations|matchers|rails)/}`, which we thought would always find the call site correctly...and then we had a case where it was considering `lib/rspec/matchers.rb` to be the call site.  Your `CallerFilter` corrected this, and I think it works properly for all cases...but I thought what we had before worked properly for all cases.  It's hard to know for sure.
* Another time, the deprecation wasn't a simple API but rather the deprecation of using an API in a particular fashion.  The logic to detect the deprecated usage is triggered later, and to print the correct call site it has to use `Proc#source_location` for the block provided by the user previously rather than relying on `CallerFilter`.  Originally, we didn't realize this and assumed that because we had the `CallerFilter` now it would print the correct call site.  It was only after I noticed the message's call site not making sense that I realized that we couldn't use `CallerFilter` for this case.

There have been other cases as well but I'm forgetting the details.

Given that we've gotten this repeatedly wrong, and how easy it is to write a test for it using the `expect_deprecation_with_call_site` helper and `__LINE__` and `__FILE__`...I think it's worth testing.