Validate Github access tokens

[sislr]

Currently, the plugin does not check whether the passed Github PAT is still valid or not. I think it would make sense to add a check in

gnosis/init.rb

Lines 6 to 11 in 4406783

	def check_env
	ENV['GITHUB_WEBHOOK_SECRET'].present? ||
	ENV['GITHUB_ACCESS_TOKEN'].present? ||
	ENV['SEMAPHORE_WEBHOOK_SECRET'].present? ||
	ENV['GITHUB_ORGANIZATION_NAME'].present?
	end

and abort if it can't be used to authorize.

[cb341]

https://renuo.slack.com/archives/CSWBT1WLA/p1733758092424389