Fix skip prompt warning (#9590)

This fixes a non-panicking log error caused by
https://github.com/zed-industries/zed/pull/9452

Release Notes:

- N/A

crates/project_panel/src/project_panel.rs

@@ -108,6 +108,7 @@ pub struct EntryDetails {
 
 #[derive(PartialEq, Clone, Default, Debug, Deserialize)]
 pub struct Delete {
+    #[serde(default)]
     pub skip_prompt: bool,
 }