This warning is pretty self- explanatory:

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@         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
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Permissions 0644 for '/Users/georg/.ssh/my_rsa_key' are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.

Solution

Limit the key to read/write access by the user only:

chmod 600 ~/.ssh/my_rsa_key

It's also possible to make it only readable by the user, but then you need to chmod every time you want to update/change it.

chmod 400 ~/.ssh/my_rsa_key

Sources: StackOverflow