Replace generic h1 find with have_selector with text filter
Replace generic h1 find with have_selector with text filter

`find('h1')` causes a race condition since it can succeed on any
page without waiting for the new response to be displayed. Rewriting
it with have_selector and `text:` filter should force Capybara to
wait until an h1 element with the correct text is present on the page.

alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests