Fix E2E test cases and setup for GHA (#26944)

* Fix E2E test cases and setup for GHA
* Fix more test cases, apply recommendations

e2e-tests/cypress/tests/integration/channels/enterprise/system_console/sidebar_link_navigation_e20_spec.js

@@ -51,7 +51,7 @@ function verifyCanNavigate(testCase) {
 
     // * Verify that it redirects to the URL and matches with the header
     cy.url().should('include', testCase.url);
-    cy.get('.admin-console__header', {timeout: TIMEOUTS.ONE_MIN}).
+    cy.get(`${testCase.headerSelector || '.admin-console__header'}`, {timeout: TIMEOUTS.ONE_MIN}).
         should('be.visible').
         and(testCase.headerContains ? 'contain' : 'have.text', testCase.header);
 }