Use PTY also with credentialStrategy=FAIL

This is a regression introduced with a199ed1396c; it is important to use a PTY
even with credentialStrategy=FAIL, otherwise the fetch command will spew the
credentials request into the UI and then hang.

This fixes the problem that background fetching makes lazygit hang when the
fetch request needs to prompt for a passphrase. For Mac users who use the
keychain to store their ssh passphrases, this can happen when lazygit is running
while the machine goes to sleep, because macOS looks the keychain in that case.

pkg/commands/oscommands/cmd_obj.go

@@ -196,6 +196,7 @@ func (self *CmdObj) PromptOnCredentialRequest(task gocui.Task) *CmdObj {
 
 func (self *CmdObj) FailOnCredentialRequest() *CmdObj {
 	self.credentialStrategy = FAIL
+	self.usePty = true
 
 	return self
 }