build: fix lint warnings

Fix warnings of the form

```
`to_string` applied to a type that implements `Display` in `format!` args
```

src/commands/gc.rs

@@ -73,7 +73,7 @@ pub fn mark_commit_reachable(repo: &Repo, commit_oid: NonZeroOid) -> eyre::Resul
         return Ok(());
     }
 
-    let ref_name = format!("refs/branchless/{}", commit_oid.to_string());
+    let ref_name = format!("refs/branchless/{}", commit_oid);
     eyre::ensure!(
         Reference::is_valid_name(&ref_name),
         format!("Invalid ref name to mark commit as reachable: {}", ref_name)

src/core/rewrite/execute.rs

@@ -690,7 +690,7 @@ mod in_memory {
         // produce a spurious abandoned-branch warning.
         let post_rewrite_stdin: String = rewritten_oids
             .iter()
-            .map(|(old_oid, new_oid)| format!("{} {}\n", old_oid.to_string(), new_oid.to_string()))
+            .map(|(old_oid, new_oid)| format!("{} {}\n", old_oid, new_oid))
             .collect();
         let post_rewrite_stdin = OsString::from(post_rewrite_stdin);
         git_run_info.run_hook(

src/git/repo.rs

@@ -854,7 +854,7 @@ Either create it, or update the main branch setting by running:
             None => {
                 let NonZeroOid { inner: oid } = oid;
                 Ok(StyledString::styled(
-                    format!("<commit not available: {}>", oid.to_string()),
+                    format!("<commit not available: {}>", oid),
                     BaseColor::Red.light(),
                 ))
             }
@@ -1455,7 +1455,7 @@ impl<'repo> Commit<'repo> {
         let preview = StyledStringBuilder::from_lines(vec![
             StyledStringBuilder::new()
                 .append_styled(
-                    format!("Commit:\t{}", self.get_oid().to_string()),
+                    format!("Commit:\t{}", self.get_oid()),
                     BaseColor::Yellow.light(),
                 )
                 .build(),