Update documentation concerning return license instructions in activation page

[GabLeRoux]

As discussed in here on Discord, Unity Hub 3.7.0 doesn't have the option to return license anymore for Personal licenses.

Step 7 in here might need an update :

Documentation:
https://game.ci/docs/github/activation/#personal-license

Source (step 7):
https://github.com/game-ci/documentation/blob/main/docs/03-github/02-activation.mdx?plain=1#L51-L53

I do confirm that the Professional license still have the Return license button:

We might suggest to return the license for Professional license activation prior to trying it in the cloud here in the docs:

https://github.com/game-ci/documentation/blob/main/docs/03-github/02-activation.mdx?plain=1#L63-L67

👍