Fix a case where "tags" is interpreted as a project slug (#7284)
Fix a case where "tags" is interpreted as a project slug (#7284)

- Assumption: There should not be a project named "tags"
- Longer term this opens up a discussion about banned project names
rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org