Delete docs directly, not api/docs

[paulbalandan]

Description
Apparently, #4969 only fixed half of the problem (which is the git reset). However, the actual contents of api/docs are not removed really. Analysing the logs from the verbose rm and mkdir, it shows that:

HEAD is now at 13c5ef1 Update README.md
mkdir: created directory 'api'
mkdir: created directory 'api/docs'

This means that instead of deleting the contents of docs in the root api, it instead looks at api/docs at the root api, a problem of relative paths. This attempts to fix the issue completely.

Successful run (in pull request context):
https://github.com/codeigniter4/CodeIgniter4/actions/runs/1075571421

Checklist:

• Securely signed commits