Revert "persistence tests: relax accuracy requirement in view of other architectures"; increase accuracy of .int reference data to 16 digits (#952)

As commented under #952 (closed), the accuracy problems seem to come from I/O, not from core numerics.

enabled an automatic merge when the pipeline for ecdd00ba succeeds

merged

mentioned in commit 1ca44bf2

@lolando can you please retrigger Debian builds, then ping me?