use ECDSA key, because GitHub dropped RSA support

[mchllngr]

The sync with GitHub fails with the error: [email protected]:[REPOSITORY].git: ERROR: You're using an RSA key with SHA-1, which is no longer allowed. Please use a newer client or a different key type.

As of March 15, 2022 GitHub permanently stopped accepting old key types (Source: https://github.blog/2021-09-01-improving-git-protocol-security-github/).

I replaced the RSA key with ECDSA-521. If the specific error returned by GitHub is recognized (by error message) the repository is removed and the user needs to add it again manually so that the new key can be deployed.