fix: use clippy::string_to_string instead of clippy:implicit_clone

```
warning: lint `clippy::string_to_string` has been removed: `clippy:implicit_clone` covers those cases
  |
  = note: requested on the command line with `-W clippy::string_to_string`
  = note: `#[warn(renamed_and_removed_lints)]` on by default
```

Author: mkroening

Cargo.toml

@@ -89,6 +89,7 @@ default_trait_access = "warn"
 explicit_deref_methods = "warn"
 if_not_else = "warn"
 ignored_unit_patterns = "warn"
+implicit_clone = "warn"
 inconsistent_struct_constructor = "warn"
 manual_assert = "warn"
 manual_let_else = "warn"
@@ -99,7 +100,6 @@ ref_as_ptr = "warn"
 ref_option = "warn"
 semicolon_if_nothing_returned = "warn"
 separated_literal_suffix = "warn"
-string_to_string = "warn"
 transmute_ptr_to_ptr = "warn"
 uninlined_format_args = "warn"
 unreadable_literal = "warn"