Do not add any label or message if the tos are already accepted

[benja-M-1]

When the issue already has the tos/accepted label, it is not necessary to add it again. Otherwise, the user will see the following weird sequence of messages

• bot: tos accepted
• bot: validation failed
• user: /validate
• bot: tos accepted
• bot: validation succeeded

Instead they will see:

• bot: tos accepted
• bot: validation failed
• user: /validate
• bot: validation succeeded