less verbose failed to parse key scan "this-is-a-bad-entry": invalid keyscan errors

[alexcb]

What existing functionality needs improvement?

echo this-is-a-bad-entry >> ~/.ssh/known_hosts
earthly github.com/earthly/earthly+base

produces:

failed to parse key scan "this-is-a-bad-entry": invalid keyscan
failed to parse key scan "this-is-a-bad-entry": invalid keyscan

Expected Behavior

We should limit this to a single line number, or possibly silence it completely (unless there's a different failure).

We should additionally print where the invalid key came from (e.g. ~/.ssh/known_hosts line X)