chore: remove React 16.4's obsolete React imports (#28571)

Signed-off-by: hainenber <dotronghai96@gmail.com>

docs/src/components/SectionHeader.tsx

@@ -16,6 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
+import { ReactNode } from 'react';
 import styled from '@emotion/styled';
 import { mq } from '../utils';
 
@@ -95,7 +96,7 @@ const StyledSectionHeaderH2 = styled(StyledSectionHeader)`
 interface SectionHeaderProps {
   level: any;
   title: string;
-  subtitle?: string | React.ReactNode;
+  subtitle?: string | ReactNode;
   dark?: boolean;
 }