ci: Switch back to Digital Ocean runners by default
The WMCS hosted GitLab CI runners are currently blocked from contacting internal Cloud VPS network addresses. The OpenTofu automation for managing Puppet Prefix settings needs to contact puppet-enc.cloudinfra.wmcloud.org. That host has a public IPv4 address, but the split-horizon DNS system used in WMCS returns the backing instance's private IPv4 address rather than the public IPv4 address. By switching back to the Digital Ocean hosted instances we are trading digital sovereignty for network access.