Clarify that only PEM key could be used (another variants will cause ssh connection error)

[idomyshev]

Bug Description
It's not clear which type of ssh key could be used

You need to write that PEM should be used
ssh-keygen -m PEM -t rsa -b 4096

[stirtingale]

This has tripped me up also.

One further thing to add. It would be good to have a idiot-proof key creation instructions in the docs

One other obvious thing is you need to add the public key (github-actions.pub) to authorized_keys so machines using the private key (github-actions) can access the server etc

i.e.

cat id_rsa.pub >> ~/.ssh/authorized_keys

[c-schmitz]

The PEM key thing is really a bummer. Bigger problem though now that newer key types do not seem to be accepted, like ed25519 . RSA keys are phased out and not accepted anymore as of Ubuntu 22, for example.
At least I tried a couple times and could not make it work.