Clarify the current JGit situation on v3.12.8

JGit cannot be supported on Gerrit stable-3.12 because of the
incompatibility of JGit's stable-7.4 with Gerrit's branch.

Provide a warning on the release notes of v3.12.8 that users upgrading
from the latest stable-3.10/3.11 of Gerrit will experience a regression
at JGit level because some of the fixes are missing.

Change-Id: Ib4bbc1957c1e3b909f3c50cde668976ec1a9a14a
1 file changed