clippy: fix stable_sort_primitive lint

https://rust-lang.github.io/rust-clippy/master/index.html#stable_sort_primitive

Part of #12343

Cargo.toml

@@ -207,6 +207,7 @@ new_without_default = "allow"
 option_map_unit_fn = "allow"
 ptr_offset_by_literal = "warn"
 ref_option = "warn"
+stable_sort_primitive = "warn"
 unnecessary_semicolon = "warn"
 
 # We do not want to use the e?print(ln)?! macros.

src/localization/settings.rs

@@ -403,7 +403,7 @@ fn add_languages<'a, 'b: 'a, LocalizationLanguage: 'a>(
     }
     add_languages(&mut language_set, fish_gettext::get_available_languages);
     let mut language_list = Vec::from_iter(language_set);
-    language_list.sort();
+    language_list.sort_unstable();
     let mut languages = WString::new();
     for lang in language_list {
         languages.push_str(lang);