test(analyzer): strengthen GB phone regression coverage

[developer0hye]

Change Description

Strengthen the regression coverage added with #2174 so it proves that PhoneRecognizer.DEFAULT_SUPPORTED_REGIONS uses the valid libphonenumber region code "GB".

The previous test reused a recognizer fixture that appends JP and CN and only checked the deduplicated result's span and score. The national-format example could therefore still match through unrelated regional passes when "GB" was reverted to the unsupported "UK" value.

This PR:

• asserts that every default region belongs to phonenumbers.SUPPORTED_REGIONS;
• runs the GB national-format case with the real default recognizer and verifies its GB textual explanation; and
• clarifies the unreleased changelog entry so it does not overstate the original behavior.

There is no production-code change. The user-facing impact is more reliable regression protection and a more precise changelog description.

Validation:

• python -m pytest tests/test_phone_recognizer.py: 28 passed
• Negative control with "GB" temporarily reverted to "UK": both new tests fail
• git diff --check: passed
• ruff check tests/test_phone_recognizer.py: reports 25 pre-existing findings on unchanged lines; the added lines have no findings

Issue reference

Fixes #2185

Checklist

• I have reviewed the contribution guidelines
• I agree to follow this project's Code of Conduct
• I confirm that I have the right to submit this contribution and that it does not knowingly contain proprietary or confidential code.
• My code includes unit tests
• All unit tests and lint checks pass locally
• My PR contains documentation updates / additions if required

[developer0hye]

The only failing CI check appears unrelated to this PR's changes.

Test Analyzer (Python 3.10) failed in the existing test_analyzer_engine_provider_no_nlp_recognizer_is_added_per_language test while spaCy attempted to download es_core_news_sm:

requests.exceptions.ConnectionError: ('Connection aborted.', ConnectionResetError(104, 'Connection reset by peer'))

The Analyzer jobs on Python 3.11, 3.13, and 3.14 passed, as did Linting. Python 3.12 was cancelled by matrix fail-fast after the Python 3.10 failure.

As an external fork contributor, I cannot rerun upstream Actions (gh reports Must have admin rights to Repository). Could a maintainer please rerun the failed and cancelled Analyzer jobs?