gh-141004: Don't trigger run-tests when Tools/check-c-api-docs/ignored_c_api.txt is changed

[StanFromIreland]

• Issue: Document the entire C API #141004

[StanFromIreland]

@hugovk maybe you could please take a look?

[ZeroIntensity]

Thanks, I'm fine with this. Since it's right before the weekend, I'll give others a few more days to take a look before merging.

[ZeroIntensity]

It might be worth keeping CONFIGURATION_FILE_NAMES and just flattening it here, but I'm not going to block the PR on it.

[hugovk]

Idle thought, we could write:

if not (doc_file or file in RUN_TESTS_IGNORE):

As:

if not doc_file and file not in RUN_TESTS_IGNORE:

I think that's a little clearer?

---

An unrelated condition that could be made clearer in this file is:

        if not has_platform_specific_change or not platforms_changed:
            a
        else:
            b

Is the same as:

        if not (has_platform_specific_change and platforms_changed):
            a
        else:
            b

And flip to put the positive first:

        if has_platform_specific_change and platforms_changed:
            b
        else:
            a