Mailer test email still contains 'Gogs'

[mjwwit]

• Gitea version (or commit ref): 8559d6f
• Git version: Not relevant
• Operating system: Not relevant
• Database: Not relevant
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist: Not relevant

Description

The Gitea Mailer test mail still contains 'Gogs' in its subject and body. Changing this to Gitea will benefit consistency.

[tboerger]

Solved via #422