feat: Add header styles inclusion

src/App.scss

@@ -10,6 +10,7 @@ $fa-font-path: "~font-awesome/fonts";
 $input-focus-box-shadow: $input-box-shadow; // hack to get upgrade to paragon 4.0.0 to work
 
 @import "~@edx/frontend-component-footer/dist/_footer";
+@import "~@edx/frontend-component-header/dist/index";
 
 #root {
   display: flex;

src/components/FilePreview/Banners/ErrorBanner.jsx

@@ -19,7 +19,7 @@ export const ErrorBanner = ({ actions, headingMessage, children }) => {
   return (
     <Alert variant="danger" icon={Info} actions={actionButtons}>
       <Alert.Heading>
-        <FormattedMessage {...headingMessage} />
+        {headingMessage ? <FormattedMessage {...headingMessage} /> : null}
       </Alert.Heading>
       {children}
     </Alert>

src/containers/ReviewModal/ReviewErrors/LockErrors.jsx

@@ -16,7 +16,7 @@ import ReviewError from './ReviewError';
  */
 export class LockErrors extends React.Component {
   get errorProp() {
-    if (this.props.errorStatus === ErrorStatuses.forbidden) {
+    if (this.props.errorStatus === ErrorStatuses.conflict) {
       return {
         heading: messages.errorLockContestedHeading,
         message: messages.errorLockContested,

src/containers/ReviewModal/ReviewErrors/LockErrors.test.jsx

@@ -42,7 +42,7 @@ describe('LockErrors component', () => {
         expect(el.instance().render()).toMatchSnapshot();
       });
       test('snapshot: error with conflicted lock', () => {
-        el.setProps({ errorStatus: ErrorStatuses.forbidden });
+        el.setProps({ errorStatus: ErrorStatuses.conflict });
         expect(el.instance().render()).toMatchSnapshot();
       });
     });