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

<!--
Thank you for contributing to Ruff! To help us out with reviewing,
please consider the following:

- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title?
- Does this pull request include references to any relevant issues?
-->

## 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_macros/src/derive_message_formats.rs

@@ -44,8 +44,8 @@ fn parse_expr(expr: &Expr, strings: &mut TokenStream) -> Result<(), TokenStream>
                     return Err(
                         quote_spanned!(expr.span() => compile_error!("prefer `String::to_string` over `format!` without arguments")),
                     );
-                };
-            };
+                }
+            }
             strings.extend(quote! {#first_token,});
             Ok(())
         }