Fix inconsistent case where datepicker fails to click (#4237)

Sometimes the full-submission tests fail on this line - it seems that the datepicker component does not always respond to .click(), and causes a timeout when the next step attempts to select today's date.

To my understanding it seems `.trigger('click')` is another approach that fares better in cases where `.click()` might fail. I have tested this many times and have yet for Cypress to break on my end with this new line.

backend/cypress/support/auditee-certification.js

@@ -13,7 +13,7 @@ export function testAuditeeCertification() {
   // 2. Sign and date, submit and go back to checklist
   cy.get('#auditee_name').type('John Doe');
   cy.get('#auditee_title').type('Auditee');
-  cy.get('.usa-date-picker__button').click();
+  cy.get('.usa-date-picker__button').trigger('click');
   cy.get('.usa-date-picker__calendar__date--today').click();
   cy.get('.usa-button').contains('Agree to auditee certification').click();
 };

backend/cypress/support/auditor-certification.js

@@ -11,7 +11,7 @@ export function testAuditorCertification() {
   // 2. Sign and date, submit and go back to checklist
   cy.get('#auditor_name').type('Jane Doe');
 	cy.get('#auditor_title').type('Auditor');
-  cy.get('.usa-date-picker__button').click();
+  cy.get('.usa-date-picker__button').trigger('click');
   cy.get('.usa-date-picker__calendar__date--today').click();
   cy.get('.usa-button').contains('Agree to auditor certification').click();
 };