`AttributeError: 'TypeVar' object has no attribute 'getattr'` with `__slots__` code

[correctmost]

Steps to reproduce

The following code triggers an AttributeError in astroid:

class C[__slots__]:
    def __init__(self):
        self.a = 1

I found the bug during a local fuzzing run.

Current behavior

Traceback (most recent call last):
  File "pylint/pylint/utils/ast_walker.py", line 87, in walk
    callback(astroid)
    ~~~~~~~~^^^^^^^^^
  File "pylint/pylint/checkers/classes/class_checker.py", line 1880, in visit_assignattr
    self._check_in_slots(node)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "pylint/pylint/checkers/classes/class_checker.py", line 1954, in _check_in_slots
    slots = safe_slots(klass)
  File "pylint/pylint/checkers/utils.py", line 1521, in safe_slots
    return node.slots()  # type: ignore[no-any-return]
           ~~~~~~~~~~^^
  File "astroid/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2822, in slots
    return self._all_slots
           ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/functools.py", line 1126, in __get__
    val = self.func(instance)
  File "astroid/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2815, in _all_slots
    slots = list(grouped_slots(mro))
  File "astroid/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2800, in grouped_slots
    cls_slots = cls._slots()
  File "astroid/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2772, in _slots
    first = next(slots)
  File "astroid/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2724, in _islots
    slots.getattr(meth)
    ^^^^^^^^^^^^^
AttributeError: 'TypeVar' object has no attribute 'getattr'

Expected behavior

No crash

Version info

cec5b897
pylint-dev/pylint@5ba4f69e7
Python 3.14.7

The crash is not reproducible with Pylint 4.0.7

Bisection data

Introduced with commit 4ea0c82 (#3058)