GitHub prohibits account name squatting (Not Reporting them), and account names may not be reserved or inactively held for future use. Accounts violating this name squatting policy may be removed or renamed without notice. Attempts to sell, buy, or solicit other forms of payment in exchange for account names are prohibited and may result in permanent account suspension.
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
But here Name Squatting Policy shows you can report inactive user which is considered as future use.
It says it's prohibited
GitHub prohibits account name squatting (Not Reporting them), and account names may not be reserved or inactively held for future use. Accounts violating this name squatting policy may be removed or renamed without notice. Attempts to sell, buy, or solicit other forms of payment in exchange for account names are prohibited and may result in permanent account suspension.