style: [AIChatInput] Set the box-sizing of inputSlot to content-box (#3095)

Author: YyumeiZhang

packages/semi-foundation/aiChatInput/aiChatInput.scss

@@ -523,6 +523,7 @@ $module: #{$prefix}-aiChatInput;
 
             .input-slot {
                 display: inline-block;
+                box-sizing: content-box;
                 background-color: $color-aiChatInput_rich_text-input_slot-bg;
                 border-radius: $radius-aiChatInput_rich_text-input_slot;
                 padding: $spacing-aiChatInput_rich_text-input_slot-paddingY $spacing-aiChatInput_rich_text-input_slot-paddingX;