[MM-61571]: Add label to form field in channel header (#29553)

* [MA-12]: Add label to form field in channel header

* [MA-12]: Update aria attributes and tests

* [MA-12]: Update snapshots, fix e2e test

* [MA-12]: Fix E2E tests

* [MA-12]: Fix type in test

e2e-tests/cypress/tests/integration/channels/channel/channel_header_modal_spec.js

@@ -36,13 +36,13 @@ describe('Channel Settings - Channel Header', () => {
             cy.findByText('Edit Channel Header').click();
 
             // # Type something in the header edit box
-            cy.get('[aria-label="edit the channel header..."]').clear().type('This is the new header content');
+            cy.get('textarea[placeholder="Edit the Channel Header..."]').clear().type('This is the new header content');
 
             // * Verify the "Preview" button exists
             cy.findByText('Preview').should('be.visible');
 
             // * Verify that before hitting the preview button, the style on the textbox is `display: block`
-            cy.get('[aria-label="edit the channel header..."]').should('have.css', 'display', 'block');
+            cy.get('textarea[placeholder="Edit the Channel Header..."]').should('have.css', 'display', 'block');
 
             // # Click the "Preview" button
             cy.findByText('Preview').click();
@@ -51,7 +51,7 @@ describe('Channel Settings - Channel Header', () => {
             cy.findByText('Edit').should('be.visible');
 
             // * Verify that the display is now none on the textbox element
-            cy.get('[aria-label="edit the channel header..."]').should('have.css', 'display', 'none');
+            cy.get('textarea[placeholder="Edit the Channel Header..."]').should('have.css', 'display', 'none');
         });
     });
 });