[SOLVED] Error in the certificate verification

package lists with `apt update`, the following error message show up: W: Failed to fetch https://deb.debian.org/debian/dists/testing/InRelease Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the

Error in the certificate verification

certificate. Could not handshake: Error in the certificate verification. [IP: 199.232.138.132 443] The IP address varies between different calls. Has anybody else encountered this problem? Gpg tells that the signature of `InRelease` is made using RSA key