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_macros/src/rule_namespace.rs

@@ -64,7 +64,7 @@ pub(crate) fn derive_impl(input: DeriveInput) -> syn::Result<proc_macro2::TokenS
             .iter()
             .find(|attr| attr.path().is_ident("doc"))
         else {
-            return Err(Error::new(variant.span(), r#"expected a doc comment"#));
+            return Err(Error::new(variant.span(), "expected a doc comment"));
         };
 
         let variant_ident = variant.ident;
@@ -155,7 +155,7 @@ fn parse_doc_attr(doc_attr: &Attribute) -> syn::Result<(String, String)> {
         .ok_or_else(|| {
             Error::new(
                 doc_lit.span(),
-                r#"expected doc comment to be in the form of `/// [name](https://example.com/)`"#,
+                "expected doc comment to be in the form of `/// [name](https://example.com/)`",
             )
         })
 }