Fix knockout icon background to match hovered entry background in project panel (#22258)

No issue attached, as this is something trivial and should have been
part of my merged PR
[here](https://github.com/zed-industries/zed/pull/22073).

For context, in the above-mentioned PR, I removed the hover color from
selected/marked entries in the Project Panel. The reasoning behind this
change is already explained in that PR, but to reiterate:

> This change was inspired by the behavior in VSCode, the Firefox
sidebar, and Dolphin (KDE File Manager). When an item is selected, it
doesn’t display a separate hover state to avoid confusing users about
whether the item is selected or merely hovered over.

@nilskch mentioned in the comments of the above PR that I should have
also changed the background of the knockout icon, which appears on
entries, to match the entry background color on hover. This PR addresses
that.

Before:

![Screenshot_20241219_230005](https://github.com/user-attachments/assets/fd517e01-1a1e-4e63-9320-ba24bf3d4c64)

After:

![Screenshot_20241219_225853](https://github.com/user-attachments/assets/35fb146f-83e4-409b-8061-0efbdbba5cf9)

Release Notes:

- N/A

crates/project_panel/src/project_panel.rs

@@ -3200,7 +3200,7 @@ impl ProjectPanel {
             item_colors.default
         };
 
-        let bg_hover_color = if self.mouse_down {
+        let bg_hover_color = if self.mouse_down || is_marked || is_active {
             item_colors.marked_active
         } else {
             item_colors.hover
@@ -3224,9 +3224,7 @@ impl ProjectPanel {
             .border_1()
             .border_r_2()
             .border_color(border_color)
-            .when(!is_marked && !is_active, |div| {
-                div.hover(|style| style.bg(bg_hover_color))
-            })
+            .hover(|style| style.bg(bg_hover_color))
             .when(is_local, |div| {
                 div.on_drag_move::<ExternalPaths>(cx.listener(
                     move |this, event: &DragMoveEvent<ExternalPaths>, cx| {