Private key is not in the correct format

I followed the [instructions](https://juliaregistries.github.io/CompatHelper.jl/dev/#Creating-SSH-Key) in the docs to set up the SSH key. But I get this [error](https://github.com/Vilin97/GradientFlows.jl/actions/runs/6739817555/job/18321961152):

```
[ Info: EnvVar `COMPATHELPER_PRIV` is defined, nonempty, and not `false`
[ Info: This doesn't look like a raw SSH private key. I will assume that it is a Base64-encoded SSH private key. I will now try to Base64-decode it.
ERROR: LoadError: Private key is not in the correct format. It must be a private key in PEM format. You should use the OpenSSH `ssh-keygen` command to generate the private key. You should pass the `-m PEM` option to ensure that the private key is in PEM format.
```

Compare the Creating-SSH-Key documentation with the COMPATHELPER_PRIV parsing and error behavior shown in the report. Reproduce the setup using the linked GitHub Actions run context; done means the documented setup is accepted without the PEM-format error.

Written by the indexing model from the issue text.