RFR: 2258: Skara won't allow "/csr unneeded" after CSR has been Withdrawn

[Zhao Song]

When processing "/csr unneeded" command, skara bot will use pr body to check if there are any open csrs  associated with the pr. However, there is a race condition here, after the user withdraws the csr, the bot needs some time to update the pr body. Therefore, if the user issues "/csr unneeded" immediately after withdrawing the csr in JBS, it's very likely that the bot would use stale pr body and make the wrong judgement.

I think the solution here is that when the bot finds existing csrs, the bot should fetch the csrs from JBS and double check if the csr issue is still open. Since the case is not very common, I believe this won't add many GET requests.

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Commit messages:
 - SKARA-2258

Changes: https://git.openjdk.org/skara/pull/1654/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1654&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2258
  Stats: 11 lines in 2 files changed: 8 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/skara/pull/1654.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1654/head:pull/1654

PR: https://git.openjdk.org/skara/pull/1654