Fix clippy::needless_borrow lint violations (#36444)

Release Notes:

- N/A

crates/git_ui/src/file_diff_view.rs

@@ -398,7 +398,7 @@ mod tests {
 
         let project = Project::test(fs.clone(), [path!("/test").as_ref()], cx).await;
 
-        let (workspace, mut cx) =
+        let (workspace, cx) =
             cx.add_window_view(|window, cx| Workspace::test_new(project.clone(), window, cx));
 
         let diff_view = workspace
@@ -417,7 +417,7 @@ mod tests {
         // Verify initial diff
         assert_state_with_diff(
             &diff_view.read_with(cx, |diff_view, _| diff_view.editor.clone()),
-            &mut cx,
+            cx,
             &unindent(
                 "
                 - old line 1
@@ -452,7 +452,7 @@ mod tests {
         cx.executor().advance_clock(RECALCULATE_DIFF_DEBOUNCE);
         assert_state_with_diff(
             &diff_view.read_with(cx, |diff_view, _| diff_view.editor.clone()),
-            &mut cx,
+            cx,
             &unindent(
                 "
                 - old line 1
@@ -487,7 +487,7 @@ mod tests {
         cx.executor().advance_clock(RECALCULATE_DIFF_DEBOUNCE);
         assert_state_with_diff(
             &diff_view.read_with(cx, |diff_view, _| diff_view.editor.clone()),
-            &mut cx,
+            cx,
             &unindent(
                 "
                   ˇnew line 1