Fixes:
```
ERROR (Net::SSH::Exception): Exception while executing on host example.com: could not settle on kex algorithm
Server kex preferences: curve25519-sha256@libssh.org,ext-info-s,kex-strict-s-v00@openssh.com
Client kex preferences: ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1```
add x25519 in Gemfile.lock
This includes a fix for a bug in the eviction thread that could cause
this error:
```
[ERROR (IOError): Exception while executing on host foo: closed stream]
```
See https://github.com/capistrano/sshkit/pull/534
1. Add Ruby 2.7 specific Gemfile that uses an older version of nokogiri
2. Rails edge doesn't support Ruby 2.7.0, so exclude it.
3. Add Ruby 3.3
4. Update Gemfile.lock to test against Rails 7.1.2 as it's the latest
version.
5. Remove continue-on-error from the matrix and always set to true
Starting many (90+) SSH connections has caused us some issues such as
failed DNS lookups and hitting process file descriptor limits.
To mitigate this, patch SSHKit::Backend::Netssh to limit concurrency of
connection starts. We'll default to 30 at a time which seems to work
without issue, but can be configured via:
```
sshkit:
max_concurrent_starts: 10
```
Versions of net-ssh before 7.0 do not support the SHA-2 algorithm and result in mrsk not being able to connect to hosts using keys generated with it. net-ssh is also a dependency of sshkit, however, sshkit has a version requirement of >= 2.8.0 for net-ssh, so is not effective at ensuring mrsk has the version it needs to be the most compatible.
