Fix AttributeError in VarAssignVisitor and cleanup test file

Move __class__ assignment check to use self.chk.fail() in VarAssignVisitor, fixing AttributeError.
Also remove temporary test comment used for triggering GitHub Actions.

Author: lsrafael13

mypy/checker.py

@@ -8882,7 +8882,7 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
             lv.accept(self)
             if isinstance(lv, MemberExpr):
                 if lv.name == '__class__':
-                    self.fail("Assignment to '__class__' is unsafe and not allowed", lv)
+                    self.chk.fail("Assignment to '__class__' is unsafe and not allowed", lv)
         self.lvalue = False
 
     def visit_name_expr(self, e: NameExpr) -> None:

test-data/unit/check-assign-to-class.test

@@ -21,4 +21,3 @@ class E:
     def baz(self):
         self.x = 2  # OK
 
-# Trigger GitHub Actions for testing