Fix crash in exim4_deliver_message_priv_esc

[adfoster-r7]

Closes #19067

Verification

Before

Method not available

>> Socket.instance_method(:expect)
(irb):1:in `instance_method': undefined method `expect' for class `Socket' (NameError)
...

After

Method available

>> Socket.instance_method(:expect)
=> #<UnboundMethod: Socket(IO)#expect(pat, timeout=...) /Users/user/metasploit-framework/lib/expect.rb:36>

[zgoldman-r7]

Release Notes

This PR fixes a bug where a user might get an unexpected NoMethodError running the linux/local/exim4_deliver_message_priv_esc module