pi@raspberrypi:~ $ sudo apt-get update
Get:1 Index of /debian/ buster InRelease [3,983 B]
Get:2 Index of /debian buster InRelease [32.6 kB]
Get:3 Index of /debian testing InRelease [116 kB]
Get:4 Index of /raspbian buster InRelease [15.0 kB]
Get:5 Index of /debian/ buster/main armhf Packages [2,507 B]
Get:6 Index of /debian buster/main armhf Packages [330 kB]
Get:7 Index of /raspbian buster/main armhf Packages [13.0 MB]
Err:3 Index of /debian testing InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 04EE7237B7D453EC NO_PUBKEY 648ACFD622F3D138
Reading package lists... Done
W: GPG error: Index of /debian testing InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 04EE7237B7D453EC NO_PUBKEY 648ACFD622F3D138
E: The repository 'Index of /debian testing InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
pi@raspberrypi:~ $
Kann mir da jemand helfen ?