Upgrade to Rust 1.86 and bump MSRV to 1.84 (#17171)

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## Summary

I decided to disable the new
[`needless_continue`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue)
rule because I often found the explicit `continue` more readable over an
empty block or having to invert the condition of an other branch.


## Test Plan

`cargo test`

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_python_ast/src/visitor.rs

@@ -276,10 +276,10 @@ pub fn walk_stmt<'a, V: Visitor<'a> + ?Sized>(visitor: &mut V, stmt: &'a Stmt) {
         }) => {
             if let Some(expr) = exc {
                 visitor.visit_expr(expr);
-            };
+            }
             if let Some(expr) = cause {
                 visitor.visit_expr(expr);
-            };
+            }
         }
         Stmt::Try(ast::StmtTry {
             body,