Add github token check

[apiraino]

I use a script to retrieve the token from a keychain, I have fumbled with the command and assigned a wrong value to the github API token. The GitHub queries then failed but the error returned by the cli tool was confusing, took me a bit to understand where the problem was.

This check ensures that the Github token retrieved is syntactically correct (a-z0-9).

cc: @spastorino

[spastorino]

I'm not sure if I'd "validate" the token in that way but 👍, I meant, whatever :)

cc @Mark-Simulacrum

[apiraino]

I'm not sure if I'd "validate" the token in that way but +1, I meant, whatever :)

right, only "syntactically correct".

What would you otherwise suggest to validate the token (without performing an actual API call)?

Anyway, it's just a papercut so it's ok to simply close it 👍 (I just thought to point it out)