Github Action to notify contributors to use Playground for PR testing.

[ankitguptaindia]

What problem does this address?

As a Test Team Representative, I've observed that new contributors prefer utilizing the Playground environment for testing core tickets instead of setting up a Local environment.

In Core ticket Pull Requests (PRs), a GitHub action automatically generates a comment regarding the use of the Playground for testing. Since Gutenberg PRs can also be tested using the Gutenberg PR testing link, it would be advantageous to include a similar message in the PR comments to facilitate easier access to the testing environment.

What is your proposed solution?

Implementing a GitHub action for Gutenberg PRs would greatly benefit new contributors by providing them with easier access to the testing environment.