Update F841 autofix to not remove line magic expr (#6141)

## Summary

Update `F841` autofix to not remove line magic expr

## Test Plan

Added test case for assignment statement with and without type
annotation

fixes: #6116

crates/ruff_python_ast/src/helpers.rs

@@ -111,6 +111,7 @@ where
                 | Expr::Subscript(_)
                 | Expr::Yield(_)
                 | Expr::YieldFrom(_)
+                | Expr::LineMagic(_)
         )
     })
 }