`ssh-keygen -t ed25519` does not support PEM key format, and it
defaults to `RFC4716` which is what we want.
It affected GHA/windows tests that explicitly used ed25519 keys.
Also:
- GHA/windows: bump minimums to hopefully catch this early next time.
1701a8319e#21353
- merge two Perl lines.
Reported-by: herbenderbler on github
Fixes#21360
Follow-up to acda4eae5e#21223Closes#21374