Django docs GitHub source links use incorrect line numbers for version branches

[Youngkwang Yang]

Django documentation uses Sphinx's .. function:: directive to generate source code links.
while these links correctly point to version-specific branches (e.g., stable/5.2.x),
the line numbers are calculated from the main branch, not the documented version.

reproduce:

1. visit Django 5.2 documentation: ​https://docs.djangoproject.com/en/5.2/ref/models/instances/#django.db.models.Model
2. click the "[source]" link
3. note the line number in the URL

current behavior:

the source link might be:
(​https://github.com/django/django/blob/stable/5.2.x/django/db/models/base.py#L498)

but in the stable/5.2.x branch, the function is actually at line 461, not 498.

expect behavior:

line number should match the actual location in the version-specific branch (e.g., L461 for stable/5.2.x).

the issue appears to be related to how line numbers are calculated during the documentation build process.
relevant code is in ​https://github.com/django/django/blob/main/docs/_ext/github_links.py#L78:
the links still work, but the inaccurate line numbers can be confusing.