Shorten class context range by one line.

Class contexts behave in some ways (tooltips, completion) as if they're
 one line longer than they ought to be:
```
a = 2
class M:
  a = "text"
b = a # tooltip of `a` says 'str', should be 'int'
a # 'int'
```
Expression-visitor doesn't have that problem, i.e. `b` is 'int' in the
 example above.

Shortening the class context range by one line fixes tooltips, uses and
 completions, and doesn't seem to break the expression visitor.

Test case "class_scope_end_outside" is fixed by this patch, the others
 are unchanged.

BUG: 309817