RFR: 1850: CSR bot can pick up wrong fix version if PR branch is behind target branch

[Zhao Song]

As SKARA-1851 fixed, now we could be able to search for CSR with the  fixVersion in .jcheck/conf from the "merge branch".

-------------

Commit messages:
 - SKARA-1850

Changes: https://git.openjdk.org/skara/pull/1496/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1496&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1850
  Stats: 142 lines in 4 files changed: 113 ins; 25 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1496.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1496/head:pull/1496

PR: https://git.openjdk.org/skara/pull/1496