Confirm that JGit 3.4.1 [Fixed JENKINS-23424]

Prior to JGit 3.4.1, tracked files which were locally modified were
not reset to their unmodified state by JGit checkout, while the CliGit
arguments used in the same cases would reset the locally modified file
to their unmodified state.
Merge commit 'fffa4c78fde695165704465af3ebe5c1652395c0' into HEAD