Fix UI font size changes not applying (#25307)

Related to #24857.

Release Notes:

- N/A

crates/assistant/src/inline_assistant.rs

@@ -2227,7 +2227,7 @@ impl PromptEditor {
             },
             font_family: settings.buffer_font.family.clone(),
             font_fallbacks: settings.buffer_font.fallbacks.clone(),
-            font_size: settings.buffer_font_size.into(),
+            font_size: settings.buffer_font_size(cx).into(),
             font_weight: settings.buffer_font.weight,
             line_height: relative(settings.buffer_line_height.value()),
             ..Default::default()