Modify the iconColor property of the Banner component to override the color. (#2575)

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## Related Issue

<!-- Please link to issue if one exists -->

<!-- Fixes #0000 -->

- resolves #2574

## Summary

<!-- Please brief explanation of the changes made -->

- 배너의 iconColor 속성을 할당해도 variant 에 의해 정해지는 색깔을 오버라이딩하지 않는 버그를 수정합니다. 

## Details

<!-- Please elaborate description of the changes -->

- iconColor 가 없을 때만 Icon classname 을 엘리먼트에 추가하도록 했습니다. 

### Breaking change? (Yes/No)

<!-- If Yes, please describe the impact and migration path for users -->

- No

## References

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- None

Author: yangwooseong

.changeset/few-singers-end.md

@@ -0,0 +1,5 @@
+---
+'@channel.io/bezier-react': patch
+---
+
+Modify the `iconColor` property of the `Banner` component to override the color.

packages/bezier-react/src/components/Banner/Banner.tsx

@@ -96,14 +96,14 @@ export const Banner = forwardRef<HTMLDivElement, BannerProps>(function Banner(
         <div className={styles.Center}>
           {isBezierIcon(icon) ? (
             <Icon
-              className={styles.Icon}
+              className={classNames(!iconColor && styles.Icon)}
               source={icon}
               color={iconColor}
               size="s"
             />
           ) : (
             <LegacyIcon
-              className={styles.Icon}
+              className={classNames(!iconColor && styles.Icon)}
               name={icon}
               color={iconColor}
               size="s"