Silence aria-descriedby warning in test (#2638)

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about the changes that needed to be released. (or didn't have to)
- [x] I wrote or updated **documentation** related to the changes. (or
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- [x] I wrote or updated **tests** related to the changes. (or didn't
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## Related Issue

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

<!-- Fixes #0000 -->

- None

## Summary

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

2개의 콘솔 warning과 error 메시지를 제거합니다. 
```Warning: Missing `Description` or `aria-describedby={undefined}` for {DialogContent}.```
``` 
`DialogContent` requires a `DialogTitle` for the component to be
accessible for screen reader users.
If you want to hide the `DialogTitle`, you can wrap it with our
VisuallyHidden component.
```


## Details

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

- DialogContent 와 연결된 described-by 가 있기를 기대하는데 ModalHeaderProps에 description 을 주지 않아서 워닝이 뜨고 있었습니다. DialogContent에 described-by={undefined} 를 추가했습니다. 
- ModalHeader 가 필요없더라도 VisuallyHidden 을 써야 접근성을 해치지 않기 때문에 명시적으로 hidden 속성을 줬습니다. 


### Breaking change? (Yes/No)

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

- No

## References

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- https://www.radix-ui.com/primitives/docs/components/dialog#description

Author: yangwooseong

packages/bezier-react/src/components/Modal/Modal.test.tsx

@@ -157,13 +157,15 @@ describe('Modal', () => {
       it("should have proper 'aria-labelledby' attribute (only title)", () => {
         const { getByRole } = renderOpenedModal({
           modalHeaderProps: { title: TITLE_TEXT, subtitle: null },
+          modalContentProps: { 'aria-describedby': undefined },
         })
         expect(getByRole('dialog', { name: TITLE_TEXT })).toBeInTheDocument()
       })
 
       it("should have proper 'aria-labelledby' attribute (hidden title)", () => {
         const { getByRole } = renderOpenedModal({
           modalHeaderProps: { title: TITLE_TEXT, subtitle: null, hidden: true },
+          modalContentProps: { 'aria-describedby': undefined },
         })
         expect(getByRole('dialog', { name: TITLE_TEXT })).toBeInTheDocument()
       })
@@ -248,6 +250,7 @@ describe('Modal', () => {
 
       it("should be visually hidden when the 'hidden' prop is true", () => {
         const { queryByRole } = renderOpenedModal({
+          modalContentProps: { 'aria-describedby': undefined },
           modalHeaderProps: { title: TITLE_TEXT, hidden: true },
         })
         /**
@@ -330,7 +333,11 @@ describe('Modal', () => {
           <ModalTrigger>
             <button type="button">{TRIGGER_TEXT}</button>
           </ModalTrigger>
-          <ModalContent>
+          <ModalContent aria-describedby={undefined}>
+            <ModalHeader
+              hidden
+              title={TITLE_TEXT}
+            />
             <ModalBody>
               <input type="text" />
             </ModalBody>