fix: Don't duplicate comments when editing TOML

`toml_edit` <0.22 has a bug that will cause
```toml
[lints]
rust.unsafe_op_in_unsafe_fn = "deny"

rust.explicit_outlives_requirements = "warn"

clippy.cast_lossless = "warn"
clippy.doc_markdown = "warn"
clippy.exhaustive_enums = "warn"
```
to be written out as
[lints]
rust.unsafe_op_in_unsafe_fn = "deny"
rust.explicit_outlives_requirements = "warn"

clippy.cast_lossless = "warn"

clippy.doc_markdown = "warn"

clippy.exhaustive_enums = "warn"
```
when it is parsed and then saved.

See toml-rs/toml#675

This affects any format-preserving edits we do, including:
- `cargo add`
- `cargo remove`
- `cargo init` / `cargo new` editing the workspace

Cargo.toml

@@ -96,8 +96,8 @@ tar = { version = "0.4.40", default-features = false }
 tempfile = "3.9.0"
 thiserror = "1.0.56"
 time = { version = "0.3", features = ["parsing", "formatting", "serde"] }
-toml = "0.8.9"
-toml_edit = { version = "0.21.1", features = ["serde"] }
+toml = "0.8.10"
+toml_edit = { version = "0.22.0", features = ["serde"] }
 tracing = "0.1.40" # be compatible with rustc_log: https://github.com/rust-lang/rust/blob/e51e98dde6a/compiler/rustc_log/Cargo.toml#L9
 tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
 unicase = "2.7.0"