Update version .jcheck/conf in jdk13u to be 13.0.8

This version is already 13.0.8 in team repo jdk13u-dev and would be changed in master after push from team to master -- but a by-product of that may be (probably), a set of duplicate backports for the fixes pushed together with that commit for JDK-8264108 "Update version .jcheck/conf in jdk13u-dev to be 13.0.8".

Price of this separate change is a merge in jdk13u-dev, so next time we should, I think, do it just after critical/security commits, immediately before pulling them to the team.