reproducibly_build_Tails_ISO_* jobs are broken

Originally created by @intrigeri on #16159 (Redmine)

Since the .img is not reproducible and diffoscope does not know any clever way to tell why, it falls back to binary diff and ends up dying because it cannot allocate memory.

For now I we should:

1. skip comparing the .img file except for feature/15985-reproducible-usb-image
2. file a ticket so that we revert this once tails#15985 (closed) is resolved and the corresponding code is merged into master→stable→devel

Feature Branch: puppet-tails:feature/always-try-to-reproduce-15985

Parent Task: #15993 (closed)

Related issues

• Related to #16162 (closed)
• Related to #16174 (closed)