It fails with missing public key.
```
08:42:44 Err:6 https://downloads.apache.org/cassandra/debian 40x InRelease
08:42:44 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 50EE103D162C5A55
08:42:44 Get:8 http://incoming.debian.org/debian-buildd buildd-unstable/main amd64 Packages [199 kB]
08:42:45 Reading package lists...
08:42:45 W: GPG error: https://downloads.apache.org/cassandra/debian 40x InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 50EE103D162C5A55
```
[1] https://jenkins.softwareheritage.org/job/debian/job/packages/job/DSTO/job/gbp-buildpackage/380/console