Youtube API key without proper referer restrictions is found in your repo. It can be embeded to anyone's website and if the billing account is active, it will incur charges on your account.
Visit following link to verify anyone can access the api key:
Attacker can abuse the key to quota exceed and cause the billing if enabled. However with the proper restrictions, it should return a Forbidden error.
Attacker is able to abuse your API key. If billing is enabled in your profile, attackers can use your key while your account gets charged.