Enable clippy::useless_format (#8758)

This PR enables the
[`clippy::useless_format`](https://rust-lang.github.io/rust-clippy/master/index.html#/useless_format)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/collab/src/db/tests/contributor_tests.rs

@@ -10,10 +10,10 @@ test_both_dbs!(
 
 async fn test_contributors(db: &Arc<Database>) {
     db.create_user(
-        &format!("user1@example.com"),
+        "user1@example.com",
         false,
         NewUserParams {
-            github_login: format!("user1"),
+            github_login: "user1".to_string(),
             github_user_id: 1,
         },
     )