RFR: 2198: Backport PRs should check if a CSR is required [v4]

[Zhao Song]

> This patch is trying to let the pr bot automatically requires csr for a backport PR if one of the associated has a resolved CSR.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  review comment

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Changes:
  - all: https://git.openjdk.org/skara/pull/1623/files
  - new: https://git.openjdk.org/skara/pull/1623/files/82f18f2d..a20024f8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1623&range=03
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1623&range=02-03

  Stats: 14 lines in 2 files changed: 6 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/skara/pull/1623.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1623/head:pull/1623

PR: https://git.openjdk.org/skara/pull/1623