Invalid mobile number field

### Description of issue
In sign-up page, mobile number input field accept lesser than 10 digits and larger than 10 digits and accept text with numbers.

```
Path: /pages/other%20pages/other%20pages/sign%20up%20page.html
Browser: Chrome 111.0.0.0 on Windows 10
Viewport: 1504 x 884 @1.5x
Language: en-GB
Cookies: Enabled
```

[Open in BrowserStack](https://www.browserstack.com/user/try-live?url=https%3A%2F%2Fdeploy-preview-1--rapid-doctor.netlify.app%2Fpages%2Fother%2520pages%2Fother%2520pages%2Fsign%2520up%2520page.html&os=Windows&os_version=10&browser=Chrome&browser_version=111.0&resolution=1504x884&speed=1&start=true&ref=netlify-source)

Submitted from [Netlify Deploy Preview #1](https://deploy-preview-1--rapid-doctor.netlify.app/pages/other%20pages/other%20pages/sign%20up%20page.html)