Appease the single_use_lifetimes lint

Unfortunately, we can't turn it on because it has false positives that
suggest a code that fails to compile, i.e.
```rust
enum Errors<'err> {
    #[error("An item with the name '{0}' already exists.")]
    ExistingItem(&'err Identifier),
    #[error("A variant referencing '{0}' already exists.")]
    ExistingVariant(&'err Identifier),
    #[error("An expression with the name '{0}' already exists.")]
    ExistingExpression(&'err Identifier),
}
```

suggests to remove the `'err` but it's impossible to define the enum
using the elided lifetime, i.e. `enum Errors<'_>`.

See rust-lang/rust#117965 for the existing bug report.

crates/codegen/parser/runtime/src/support/context.rs

@@ -120,14 +120,14 @@ pub(crate) struct DelimiterGuard<'a, 's> {
     closing_delim: TokenKind,
 }
 
-impl<'a, 's> Drop for DelimiterGuard<'a, 's> {
+impl Drop for DelimiterGuard<'_, '_> {
     fn drop(&mut self) {
         let popped = self.input.closing_delimiters.pop();
         debug_assert_eq!(popped, Some(self.closing_delim));
     }
 }
 
-impl<'a, 's> DelimiterGuard<'a, 's> {
+impl<'s> DelimiterGuard<'_, 's> {
     pub(crate) fn ctx(&mut self) -> &mut ParserContext<'s> {
         self.input
     }