button: Fix loading style when disabled. (#1021)

## Before

<img width="1193" alt="image"
src="https://github.com/user-attachments/assets/e7a82f21-2ec8-42fa-8daa-05d4f086e0b2"
/>

## After

<img width="1196" alt="image"
src="https://github.com/user-attachments/assets/f387c591-a4a1-4220-9318-badfb8a133e6"
/>

crates/ui/src/button/button.rs

@@ -520,7 +520,11 @@ impl RenderOnce for Button {
                     })
                     .children(self.children)
             })
-            .when(self.loading, |this| this.bg(normal_style.bg.opacity(0.8)))
+            .when(self.loading && !self.disabled, |this| {
+                this.bg(normal_style.bg.opacity(0.8))
+                    .border_color(normal_style.border.opacity(0.8))
+                    .text_color(normal_style.fg.opacity(0.8))
+            })
             .when_some(self.tooltip, |this, (tooltip, action)| {
                 this.tooltip(move |window, cx| {
                     Tooltip::new(tooltip.clone())