Changed types to be more specific

Signed-off-by: John Philip <johnphilip283@gmail.com>

packages/core-components/src/components/MarkdownContent/MarkdownContent.tsx

@@ -20,6 +20,7 @@ import gfm from 'remark-gfm';
 import React from 'react';
 import { BackstageTheme } from '@backstage/theme';
 import { CodeSnippet } from '../CodeSnippet';
+import { HeadingProps } from 'react-markdown/lib/ast-to-react';
 
 export type MarkdownContentClassKey = 'markdown';
 
@@ -73,13 +74,15 @@ type Props = {
   className?: string;
 };
 
-const flatten = (text, child) => {
+const flatten = (text: string, child: any): string => {
+  if (!child) return text;
+
   return typeof child === 'string'
     ? text + child
     : React.Children.toArray(child.props.children).reduce(flatten, text);
 };
 
-const headingRenderer = ({ level, children }) => {
+const headingRenderer = ({ level, children }: HeadingProps) => {
   const childrenArray = React.Children.toArray(children);
   const text = childrenArray.reduce(flatten, '');
   const slug = text.toLocaleLowerCase('en-US').replace(/\W/g, '-');