Update to Rust 1.74 and use new clippy lints table (#8722)

Update to [Rust
1.74](https://blog.rust-lang.org/2023/11/16/Rust-1.74.0.html) and use
the new clippy lints table.

The update itself introduced a new clippy lint about superfluous hashes
in raw strings, which got removed.

I moved our lint config from `rustflags` to the newly stabilized
[workspace.lints](https://doc.rust-lang.org/stable/cargo/reference/workspaces.html#the-lints-table).
One consequence is that we have to `unsafe_code = "warn"` instead of
"forbid" because the latter now actually bans unsafe code:

```
error[E0453]: allow(unsafe_code) incompatible with previous forbid
  --> crates/ruff_source_file/src/newlines.rs:62:17
   |
62 |         #[allow(unsafe_code)]
   |                 ^^^^^^^^^^^ overruled by previous forbid
   |
   = note: `forbid` lint level was set on command line
```

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/ruff_python_formatter/src/expression/string.rs

@@ -51,7 +51,7 @@ impl<'a> AnyString<'a> {
                     .slice(f_string.range)
                     .trim_start_matches(|c| c != '"' && c != '\'');
                 let triple_quoted =
-                    unprefixed.starts_with(r#"""""#) || unprefixed.starts_with(r#"'''"#);
+                    unprefixed.starts_with(r#"""""#) || unprefixed.starts_with(r"'''");
                 if f_string.values.iter().any(|value| match value {
                     Expr::FormattedValue(ast::ExprFormattedValue { range, .. }) => {
                         let string_content = locator.slice(*range);