fix: Fix unit tests failing with release branch env variable

[mgwozdz-unicon]

Description

My Verawood PR has unit tests failing on what appears to be an unrelated environment variable issue:

FAILED lms/djangoapps/mfe_config_api/tests/test_views.py::MFEConfigTestCase::test_legacy_overrides_instructor_dashboard - AssertionError: 'https://docs.openedx.org/en/open-release-verawood.master/educators/index.html' != 'https://docs.openedx.org/en/latest/educators/index.html'
- https://docs.openedx.org/en/open-release-verawood.master/educators/index.html
?                             ^^ ---------------------  --
+ https://docs.openedx.org/en/latest/educators/index.html
?                             ^^^
FAILED lms/djangoapps/mfe_config_api/tests/test_views.py::FrontendSiteConfigTestCase::test_legacy_overrides_instructor_dashboard_support_url - AssertionError: 'https://docs.openedx.org/en/open-release-verawood.master/educators/index.html' != 'https://docs.openedx.org/en/latest/educators/index.html'
- https://docs.openedx.org/en/open-release-verawood.master/educators/index.html
?                             ^^ ---------------------  --
+ https://docs.openedx.org/en/latest/educators/index.html
?                             ^^^

Supporting information

This is blocking getting #38495 into the Verawood release.

Testing instructions

python -m pytest lms/djangoapps/mfe_config_api/tests/test_views.py

Deadline

This is blocking getting #38495 into the Verawood release.

[openedx-webhooks]

Thanks for the pull request, @mgwozdz-unicon!

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[wgu-taylor-payne]

The fix makes sense — the hardcoded "latest" breaks on release branches where doc_version() returns "open-release-verawood.master".

How the URL is constructed

The SUPPORT_URL flows through four layers:

1. View layer — views.py: get_legacy_config_overrides() calls resolve_help_token("instructor") → HelpUrlExpert.the_one().url_for_token("instructor")
2. help-tokens library — url_for_token() reads help_tokens.ini (instructor = course_author:index.html), looks up HELP_TOKENS_BOOKS["course_author"], then replaces /latest with /{version}
3. Settings — common.py: HELP_TOKENS_VERSION = Derived(lambda settings: doc_version())
4. Release info — release.py: doc_version() returns "latest" on master, "open-release-{RELEASE_LINE}.master" on release branches

See inline suggestion for a slightly more precise alternative approach.

Review assisted by Kiro

[wgu-taylor-payne]

Looks good, thanks for this! Do you plan to make a backport PR for this @mgwozdz-unicon?

[feanil]

Backport PR for verawood: #38503