Enable excessibility checking of login menu, and remove unnecessary exclusion from header

(cherry picked from commit 339ed63)

Author: tdonohue

cypress/e2e/header.cy.ts

@@ -11,8 +11,7 @@ describe('Header', () => {
         testA11y({
             include: ['ds-header'],
             exclude: [
-                ['#search-navbar-container'], // search in navbar has duplicative ID. Will be fixed in #1174
-                ['.dropdownLogin']            // "Log in" link has color contrast issues. Will be fixed in #1149
+                ['#search-navbar-container'] // search in navbar has duplicative ID. Will be fixed in #1174
             ],
         });
     });

cypress/e2e/login-modal.cy.ts

@@ -1,4 +1,5 @@
 import { TEST_ADMIN_PASSWORD, TEST_ADMIN_USER, TEST_ENTITY_PUBLICATION } from 'cypress/support/e2e';
+import { testA11y } from 'cypress/support/utils';
 
 const page = {
     openLoginMenu() {
@@ -123,4 +124,15 @@ describe('Login Modal', () => {
         cy.location('pathname').should('eq', '/forgot');
         cy.get('ds-forgot-email').should('exist');
     });
+
+    it('should pass accessibility tests', () => {
+        cy.visit('/');
+
+        page.openLoginMenu();
+
+        cy.get('ds-log-in').should('exist');
+
+        // Analyze <ds-log-in> for accessibility issues
+        testA11y('ds-log-in');
+    });
 });