[DOC] section on new tests in PULL_REQUEST_TEMPLATE

[Aarthy153]

Description
Added a separate section to ask contributors whether they have added any new tests.

Issue
#4066

[Aarthy153]

Hi, @achieveordie I have successfully set up the dev environment with the help of the guide. I have made these commits from my local machine and created a new PR. Please check and guide me. Thank you!

[achieveordie]

The first check has passed which means the dev environment was set up properly. I'd recommend you not change the template when you're making a PR (instead leave the irrelevant parts blank and add new parts as you see fit) since it doesn't link this PR to the original issue and we'll have to manually close that issue once this PR merges.

Content-wise, everything looks good to me. Although I think we can now remove the third point inside "For all contributors" which asks "I've added unit tests and made sure they pass locally" since that is being moved to its own subsection.

[Aarthy153]

@achieveordie Will follow the PR template from here on. Thanks for the section! By the way, I have removed the third point under the 'For all contributors section'. Kindly check. Thank you!