Use serde 1.0.221 instead of serde_derive hackery (#38137)

serde 1.0.221 introduced serde_core into the build graph, which should
render explicitly depending on serde_derive for faster build times an
obsolote method.

Besides, I'm not even sure if that worked for us. My hunch is that at
least one of our deps would have `serde` with derive feature enabled..
and then, most of the crates using `serde_derive` explicitly were also
depending on gpui, which depended on `serde`.. thus, we wouldn't have
gained anything from explicit dep on `serde_derive`

Release Notes:

- N/A

crates/settings/src/settings_store.rs

@@ -1588,7 +1588,7 @@ mod tests {
     use super::*;
     // This is so the SettingsUi macro can still work properly
     use crate as settings;
-    use serde_derive::Deserialize;
+    use serde::Deserialize;
     use settings_ui_macros::{SettingsKey, SettingsUi};
     use unindent::Unindent;
 
@@ -2232,7 +2232,9 @@ mod tests {
 
     #[derive(Debug, Deserialize)]
     struct JournalSettings {
+        #[expect(unused)]
         pub path: String,
+        #[expect(unused)]
         pub hour_format: HourFormat,
     }