Ambiguous handling of multiple keys when allow_missing_kid and no_kid_issuer are not set

[lionick]

In the _add_key method, when multiple keys (_add_keys) are retrieved for an issuer but neither allow_missing_kid is True nor no_kid_issuer is provided for the issuer, the function does not add any keys to the keys list. This situation leads to silent failure, with no keys added.

Here is the part of the code:
https://github.com/IdentityPython/JWTConnect-Python-CryptoJWT/blob/main/src/cryptojwt/key_jar.py#L491