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/settings/display/theme/code_theme_colors_spec.js

@@ -35,7 +35,7 @@ describe('Settings > Display > Theme > Custom Theme Colors', () => {
             cy.get('#customThemes').check().should('be.checked');
 
             // # Open Center Channel Styles section
-            cy.get('#centerChannelStyles').click({force: true});
+            cy.get('#centerChannelStyles').click({force: true}).wait(TIMEOUTS.ONE_HUNDRED_MILLIS);
 
             // # Select custom code theme
             cy.get('#codeThemeSelect').scrollIntoView().should('be.visible').select(theme.name);