Fix iterator related clippy style lint violations (#36437)

Release Notes:

- N/A

crates/git_ui/src/git_panel.rs

@@ -2756,7 +2756,7 @@ impl GitPanel {
         for pending in self.pending.iter() {
             if pending.target_status == TargetStatus::Staged {
                 pending_staged_count += pending.entries.len();
-                last_pending_staged = pending.entries.iter().next().cloned();
+                last_pending_staged = pending.entries.first().cloned();
             }
             if let Some(single_staged) = &single_staged_entry {
                 if pending
@@ -5261,7 +5261,7 @@ mod tests {
             project
                 .read(cx)
                 .worktrees(cx)
-                .nth(0)
+                .next()
                 .unwrap()
                 .read(cx)
                 .as_local()
@@ -5386,7 +5386,7 @@ mod tests {
             project
                 .read(cx)
                 .worktrees(cx)
-                .nth(0)
+                .next()
                 .unwrap()
                 .read(cx)
                 .as_local()
@@ -5437,7 +5437,7 @@ mod tests {
             project
                 .read(cx)
                 .worktrees(cx)
-                .nth(0)
+                .next()
                 .unwrap()
                 .read(cx)
                 .as_local()
@@ -5486,7 +5486,7 @@ mod tests {
             project
                 .read(cx)
                 .worktrees(cx)
-                .nth(0)
+                .next()
                 .unwrap()
                 .read(cx)
                 .as_local()

crates/git_ui/src/project_diff.rs

@@ -280,7 +280,7 @@ impl ProjectDiff {
     fn button_states(&self, cx: &App) -> ButtonStates {
         let editor = self.editor.read(cx);
         let snapshot = self.multibuffer.read(cx).snapshot(cx);
-        let prev_next = snapshot.diff_hunks().skip(1).next().is_some();
+        let prev_next = snapshot.diff_hunks().nth(1).is_some();
         let mut selection = true;
 
         let mut ranges = editor