Remove unneeded 'static lifetimes on &strs in constants (#8698)

This PR removes unneeded `'static` lifetimes on `&str`s stored in
`const` declarations.

This addresses some Clippy lints about
[`redundant_static_lifetimes`](https://rust-lang.github.io/rust-clippy/master/index.html#/redundant_static_lifetimes).

In item-level `const` declarations we can rely on lifetime elision and
use the default `'static` lifetime.

Note that associated constants still require an explicit `'static`
lifetime, as explained in
https://github.com/rust-lang/rust/issues/115010.

Release Notes:

- N/A

crates/collab/src/tests/integration_tests.rs

@@ -2821,8 +2821,8 @@ async fn test_git_status_sync(
         )
         .await;
 
-    const A_TXT: &'static str = "a.txt";
-    const B_TXT: &'static str = "b.txt";
+    const A_TXT: &str = "a.txt";
+    const B_TXT: &str = "b.txt";
 
     client_a.fs().set_status_for_repo_via_git_operation(
         Path::new("/dir/.git"),