chore: Bump Rust version to 1.88 (#33439)

Goodies in this version:
- if-let chains 🎉
- Better compiler perf for Zed
(https://github.com/rust-lang/rust/pull/138522)

For more, see: https://releases.rs/docs/1.88.0/

Release Notes:

- N/A

---------

Co-authored-by: Junkui Zhang <364772080@qq.com>

crates/project/src/git_store/conflict_set.rs

@@ -565,7 +565,7 @@ mod tests {
             conflict_set.snapshot().conflicts[0].clone()
         });
         cx.update(|cx| {
-            conflict.resolve(buffer.clone(), &[conflict.theirs.clone()], cx);
+            conflict.resolve(buffer.clone(), std::slice::from_ref(&conflict.theirs), cx);
         });
 
         cx.run_until_parked();