fix(dashboard-css): make to stay custom css when reload (#19084)

* fix(dashboard-css): make to stay custome css when reload

* fix(dashboard-css): make to add injectCustomCSS into HeaderActionsDropdown.test.tsx

(cherry picked from commit 30c97ad)

superset-frontend/src/dashboard/components/Header/HeaderActionsDropdown/HeaderActionsDropdown.test.tsx

@@ -21,6 +21,7 @@ import { render, screen } from 'spec/helpers/testing-library';
 import userEvent from '@testing-library/user-event';
 import fetchMock from 'fetch-mock';
 import { HeaderDropdownProps } from 'src/dashboard/components/Header/types';
+import injectCustomCss from 'src/dashboard/util/injectCustomCss';
 import HeaderActionsDropdown from '.';
 
 const createProps = () => ({
@@ -180,7 +181,9 @@ test('should NOT render the "Refresh dashboard" menu item as disabled', async ()
 
 test('should render with custom css', () => {
   const mockedProps = createProps();
+  const { customCss } = mockedProps;
   render(setup(mockedProps));
+  injectCustomCss(customCss);
   expect(screen.getByRole('button')).toHaveStyle('margin-left: 100px');
 });
 

superset-frontend/src/dashboard/components/Header/HeaderActionsDropdown/index.jsx

@@ -117,8 +117,6 @@ class HeaderActionsDropdown extends React.PureComponent {
   }
 
   UNSAFE_componentWillMount() {
-    injectCustomCss(this.state.css);
-
     SupersetClient.get({ endpoint: '/csstemplateasyncmodelview/api/read' })
       .then(({ json }) => {
         const cssTemplates = json.result.map(row => ({