Investigate adding back skipped E2E tests

[dkotter]

Is your enhancement related to a problem? Please describe.

While prepping the 1.8.0 release, noticed there are a handful of comments in our test files that mention a few tests are being skipped but should be fixed in the 1.7.0 release.

I didn't spend anytime to see if those tests run but seems worthwhile to investigate these, check if these tests now pass and if so, add them back.

• wordpress/tests/cypress/e2e/submission/js-submission.test.js

  Line 89 in 359123e

  // TODO: BUG: Single opt-in is currently broken, but a fix is scheduled for 1.7.0

• wordpress/tests/cypress/e2e/submission/subscribe.test.js

  Line 34 in e993e48

  // // TODO: This is failing because of a bug causing single opt-in to malfunction. Fix is ready for 1.7.0.

• wordpress/tests/cypress/e2e/submission/update-subscribers.test.js

  Lines 92 to 94 in 359123e

  	// TODO: This test is correct, but failing to a bug allowing contacts to be updated
  	// regardless of the "Update Existing Subscriber?" option
  	// Fix in issue 113 scheduled for 1.7.0.

• wordpress/tests/cypress/e2e/validation/us-phone.test.js

  Lines 8 to 11 in 359123e

  	// TODO: BUG: Skipping for now because when a US phone number is selected in the Mailchimp account, but
  	// not present on the webform there will always be a fatal error. There is a fix pending for 1.7.0.
  	// TODO: Skipping for now because the Mailchimp API does not allow changing the format for a phone merge
  	// field to the US style

Designs

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Describe alternatives you've considered

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