Upgrade dogfood GHE to 2.22.6

Created by: pecigonzalo

To help troubleshoot and develop a fix for https://github.com/sourcegraph/sourcegraph/issues/17153 we need to be able to use the "internal" visibility option which according to GitHub docs should be supported in GHE 2.20+ but our GHE test instance (2.20.8) doesn't have it as pointed out in the linked issue.

The upgrade process is described in https://docs.github.com/en/[email protected]/admin/enterprise-management/upgrading-github-enterprise-server and seems to be quite straight forward.

TODO

• Enable maintenance mode
• Snapshot
• Upgrade
• Check