[Sign up as a tutor popup] Verify that the 'Sing Up' button is active when all fields are filled out with correct data.

**Priority** medium

**Description**
This test verifies that the 'Sing Up' button is active when all fields are filled out with correct data.

**Preconditions**
The https://s2s-front-stage.azurewebsites.net/ site is opened.
The button "Become a Tutor" is clicked and "Sign Up" pop-up appeared.

**Steps to reproduce**
1. Fill the fields
‘First name’
‘Last name’
‘Email’
‘Password’
‘Confirm ‘Password’
‘Agreement box’
with correct data
2. Tick the checkbox.

**Expected result**
The 'Sing Up' button is active.

Epic #29

Open the staging site and use the “Become a Tutor” button to reach the “Sign Up” popup. Fill First name, Last name, Email, Password, Confirm Password, and the agreement checkbox with valid data, then verify that the “Sign Up” button becomes active; record the result against the expected behavior.

Written by the indexing model from the issue text.