Upgrade toml to v0.8 (#7931)

This PR upgrades our `toml` dependency to v0.8.

I noticed that our current version of `toml` wasn't able to parse
certain kinds of documents involving enums, whereas the newer version
can.

Release Notes:

- N/A

crates/extension/src/extension_store.rs

@@ -415,8 +415,8 @@ impl ExtensionStore {
                 language.matcher.clone(),
                 vec![],
                 move || {
-                    let config = std::fs::read(language_path.join("config.toml"))?;
-                    let config: LanguageConfig = ::toml::from_slice(&config)?;
+                    let config = std::fs::read_to_string(language_path.join("config.toml"))?;
+                    let config: LanguageConfig = ::toml::from_str(&config)?;
                     let queries = load_plugin_queries(&language_path);
                     Ok((config, queries))
                 },