Attempt to fix issue with ParamSpec serialization (#12654)
I've seen crashes like this, which might be caused by not
fixing up some FakeInfos:
```
File "mypy/checkexpr.py", line 3981, in accept
File "mypy/nodes.py", line 1753, in accept
File "mypy/checkexpr.py", line 288, in visit_call_expr
File "mypy/checkexpr.py", line 371, in visit_call_expr_inner
File "mypy/checkexpr.py", line 880, in check_call_expr_with_callee_type
File "mypy/checkexpr.py", line 940, in check_call
File "mypy/checkexpr.py", line 1027, in check_callable_call
File "mypy/checkexpr.py", line 1269, in infer_function_type_arguments
File "mypy/checkexpr.py", line 1324, in infer_function_type_arguments_pass2
File "mypy/infer.py", line 47, in infer_function_type_arguments
File "mypy/constraints.py", line 72, in infer_constraints_for_callable
File "mypy/constraints.py", line 108, in infer_constraints
File "mypy/constraints.py", line 181, in _infer_constraints
File "mypy/types.py", line 1576, in accept
File "mypy/constraints.py", line 663, in visit_callable_type
File "mypy/constraints.py", line 685, in infer_against_overloaded
File "mypy/constraints.py", line 775, in find_matching_overload_item
File "mypy/subtypes.py", line 942, in is_callable_compatible
File "mypy/subtypes.py", line 1209, in unify_generic_callable
File "mypy/applytype.py", line 86, in apply_generic_arguments
File "mypy/applytype.py", line 50, in get_target_type
File "mypy/subtypes.py", line 97, in is_subtype
File "mypy/subtypes.py", line 158, in _is_subtype
File "mypy/types.py", line 615, in accept
File "mypy/subtypes.py", line 341, in visit_param_spec
File "mypy/subtypes.py", line 217, in _is_subtype
File "mypy/subtypes.py", line 97, in is_subtype
File "mypy/subtypes.py", line 158, in _is_subtype
File "mypy/types.py", line 1127, in accept
File "mypy/subtypes.py", line 257, in visit_instance
AttributeError: attribute 'fallback_to_any' of 'TypeInfo' undefined
```
I don't have a small reproducer to I couldn't add a test case,
unfortunately.
