package-source-builder: APT debugging to catch hash mismatches

We keep getting hard-to-debug hash mismatches when downloading packages with APT, like this one in the https://gitlab.apertis.org/pkg/target/ostree/-/jobs/189090 GitLab pipeline:

Err:94 https://repositories.apertis.org/apertis v2020dev0/target amd64 libsystemd-dev amd64 241-5co3bv2020dev0b1
  Hash Sum mismatch
  Hashes of expected file:
   - SHA256:41d1ccfd064d8e7aafd19d031f0f35e350279dec3e46c2d6323b9a70159a5bd4
   - SHA1:161fff18c277d0b8bda8a80be7a433e8807aca13 [weak]
   - MD5Sum:2ae73e29e95daa715d07ac2b1ca78412 [weak]
   - Filesize:320672 [weak]
  Hashes of received file:
   - SHA256:bba2cd8458b872069ec6697f2ec23ee47ab5e285d6627f96b6d44914d61c0f14
   - SHA1:384222001e9c4a63552e0017da7aadee5894344b [weak]
   - MD5Sum:63b6130dcff030abf9c75a91074b6731 [weak]
   - Filesize:320672 [weak]
  Last modification reported: Thu, 15 Aug 2019 18:46:42 +0000
Get:95 https://repositories.apertis.org/apertis v2020dev0/target amd64 libyaml-0-2 amd64 0.2.1-1ba1 [49.2 kB]
Get:96 https://repositories.apertis.org/apertis v2020dev0/development amd64 python3-yaml amd64 3.13-2bv2020dev0b1 [121 kB]
E: Failed to fetch https://repositories.apertis.org/apertis/pool/target/s/systemd/libsystemd-dev_241-5co3bv2020dev0b1_amd64.deb  Hash Sum mismatch
   Hashes of expected file:
    - SHA256:41d1ccfd064d8e7aafd19d031f0f35e350279dec3e46c2d6323b9a70159a5bd4
    - SHA1:161fff18c277d0b8bda8a80be7a433e8807aca13 [weak]
    - MD5Sum:2ae73e29e95daa715d07ac2b1ca78412 [weak]
    - Filesize:320672 [weak]
   Hashes of received file:
    - SHA256:bba2cd8458b872069ec6697f2ec23ee47ab5e285d6627f96b6d44914d61c0f14
    - SHA1:384222001e9c4a63552e0017da7aadee5894344b [weak]
    - MD5Sum:63b6130dcff030abf9c75a91074b6731 [weak]
    - Filesize:320672 [weak]
   Last modification reported: Thu, 15 Aug 2019 18:46:42 +0000

It also happens on Jenkins and has been intermittently reproduced on developer machines.

Only APT seems to be affected, so enable as much debugging we can to try to catch it.

See https://phabricator.collabora.com/T15071 for more information.