Update certbot requirement from <6.0,>=1.18.0 to >=5.6.0,<6.0

Updates the requirements on [certbot](https://github.com/certbot/certbot) to permit the latest version.
- [Release notes](https://github.com/certbot/certbot/releases)
- [Commits](certbot/certbot@v1.18.0...v5.6.0)

---
updated-dependencies:
- dependency-name: certbot
  dependency-version: 5.6.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,4 +1,4 @@
 setuptools>=41.6.0
 requests>=2.20.0,<3.0
-certbot>=1.18.0,<6.0
+certbot>=5.6.0,<6.0
 dnspython>=1.15.0,<3.0