Eclipse Californium (Cf) CoAP Framework 2.8.0

Minor release.

Contains a bugfix for the client side observe function (RFC 7641)

Update of dependencies. Some of the dependencies may be considered to be part of API, therefore it's a minor release. The code in californium itself hasn't changed the API:

2e44e3ad2 2023-06-26 Update dependencies.

4dab6e0a3 2023-02-07 back-port fixes for client side observe.

5220bb083 2022-10-26 Renew demo certificates.

2023ccdb4 2022-09-21 2.7.5-SNAPSHOT after release 2.7.4