Fix two clippy issues

Cargo.toml

@@ -24,8 +24,8 @@ sign-tag = true
 tag = false
 
 [workspace.lints.rust]
+rust_2018_idioms = { level = "warn", priority = -1 }
 missing_docs = "warn"
-rust_2018_idioms = "warn"
 trivial_casts = "warn"
 trivial_numeric_casts = "warn"
 unused_extern_crates = "warn"

serde_with_macros/src/lib.rs

@@ -538,8 +538,7 @@ fn field_has_attribute(field: &Field, namespace: &str, name: &str) -> bool {
 ///     If `#[serde(borrow)]` or `#[serde(borrow = "...")]` is already present, this step will be
 ///     skipped.
 ///
-/// 5. Restore the ability of accepting missing fields if both the field and the
-/// transformation are `Option`.
+/// 5. Restore the ability of accepting missing fields if both the field and the transformation are `Option`.
 ///
 ///     An `Option` is detected by an exact text match.
 ///     Renaming an import or type aliases can cause confusion here.