Fixing "Environment variable not found"

Dependencies

• [2] SZWBLWZ4 Reading ~/.ssh/config
• [3] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).
• [4] MU6P2JXG SSH: return with an error if the host key is wrong, rather than denying authentication

Change contents

• replacement in pijul/src/remote/ssh.rs at line 128
  [3.28944]→[3.28944:29032](∅→∅)
  − let mut agent = thrussh_keys::agent::client::AgentClient::connect_env().await?;
  [3.28944]

  [2.1096]
  + let mut agent = match thrussh_keys::agent::client::AgentClient::connect_env().await {

  + Ok(agent) => agent,

  + Err(thrussh_keys::Error::EnvVar(_)) => return Ok(false),

  + Err(e) => return Err(e.into()),

  + };