fix migration test

apps/remix-ide-e2e/src/tests/migrateFileSystem.test.ts

@@ -8,7 +8,7 @@ module.exports = {
   },
   'Should have README file with TEST README as content': function (browser: NightwatchBrowser) {
     browser.waitForElementVisible('*[data-id="remixIdeSidePanel"]', 5000)
-      .click('*[data-id="verticalIconsFileExplorerIcons"]')
+      .waitForElementVisible('div[data-id="filePanelFileExplorerTree"]')
       .openFile('TEST_README.txt')
       .getEditorValue((content) => {
         browser.assert.equal(content, 'TEST README')