website cache should be keyed on debian/changelog
Originally created by @intrigeri on #17511 (Redmine)
Otherwise, for example we can hit this scenario:
- during a built from the stable branch, the website is built with
SOURCE_DATE_EPOCH
derived from the last changelog entry on that branch (date1); the result of that build is cached - during another build from the devel branch, on a different
isobuilder, the website is built with
SOURCE_DATE_EPOCH
derived from the last changelog entry on that branch (date2); the result of that build is cached - when Jenkins tries to reproduce build 2, on the same isobuilder as build 1, our build system reuses the website built with date1, which does not match the website built with date2 during build 2 ⇒ different images, reproducibility check fails
Feature Branch: bugfix/17511-website-cache-vs-differing-changelog-entries