Fix: instance variables link to other variables of the same name

[piyushhhxyz]

Summary

Removes rolename='obj' from the 'variable' PyTypedField definition in sphinx/domains/python.py so that variable names documented with :var:, :ivar:, or :cvar: are no longer automatically turned into cross-reference links.

Problem

When using autodoc (especially via apidoc), instance variables documented with :ivar: or :var: had their names automatically wrapped in pending_xref nodes with role obj. This caused Sphinx's cross-reference resolution (including fuzzy matching in find_obj) to link them to completely unrelated variables with the same name elsewhere in the project.

For example, somepackage.subA.Foo.limit would auto-link to somepackage.subB.Bar.limit even though they are completely unrelated.

Fix

Removed rolename='obj' from the variable field type definition:

# Before
PyTypedField('variable', label=_('Variables'), rolename='obj',
             names=('var', 'ivar', 'cvar'),
             typerolename='class', typenames=('vartype',),
             can_collapse=True),

# After  
PyTypedField('variable', label=_('Variables'),
             names=('var', 'ivar', 'cvar'),
             typerolename='class', typenames=('vartype',),
             can_collapse=True),

The typerolename='class' is preserved, so variable types are still cross-referenced as expected. Only the variable names stop being auto-linked.

Fixes #8638