RFR: 2214: Require CSR again if all of the CSRs are withdrawn in a Backport CSR PR

[Zhao Song]

When testing [SKARA-2198](https://bugs.openjdk.org/browse/SKARA-2198), I found that there is a bug.

When determining if the bot should add the csr label to a backport CSR pr, if the bot found the pr is already associated with any CSR(regardless if it's withdrawn or not), then the bot would not add the csr label.

This is a bug. A user could create a CSR for this pr and withdraw it, then the user could bypass the CSR request.

The bot should ignore withdrawn CSRs in this case.

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Commit messages:
 - SKARA-2214

Changes: https://git.openjdk.org/skara/pull/1625/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1625&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2214
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1625.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1625/head:pull/1625

PR: https://git.openjdk.org/skara/pull/1625