fix: check no "ERR!" string is in stderr when running Storybook build (…

…redwoodjs#3509)

* fix: check no "ERR!" string is in stderr

Avoid false positive

Seems stderr is used for info as well as error

see: https://github.com/redwoodjs/redwood/runs/3799459178?check_suite_focus=true

* fix: use .then

hope to avoid `Cannot read properties of undefined (reading 'split')`
see: https://github.com/redwoodjs/redwood/runs/3802028363?check_suite_focus=true

Co-authored-by: David Price <thedavid@thedavidprice.com>

tasks/e2e/cypress/integration/03-storybook/storybook.spec.js

@@ -32,14 +32,14 @@ describe(
         Step2_2_BlogPostsCellMock
       )
 
+      // Slow!
       cy.exec(`cd ${BASE_DIR}; yarn rw storybook --build`, {
         timeout: 300_0000,
-      }) // Slow!
-        .its('stderr')
-        .should('eq', '')
-        .and()
-        .its('code')
-        .should('eq', 0)
+      }).then((result) => {
+        const { code, stderr } = result
+        expect(code).to.eq(0)
+        expect(stderr).to.not.contain('ERR!')
+      })
     })
 
     it('1. Component: BlogPost', () => {