Use const over static for string literals (#18635)

I noticed a few places where we were storing `&'static str`s in
`static`s instead of `const`s.

This PR updates them to use `const`.

Release Notes:

- N/A

crates/worktree/src/worktree.rs

@@ -351,7 +351,7 @@ pub enum Event {
     DeletedEntry(ProjectEntryId),
 }
 
-static EMPTY_PATH: &str = "";
+const EMPTY_PATH: &str = "";
 
 impl EventEmitter<Event> for Worktree {}