RFR: 1612: Temp workaround GitLab returning 500 when modifying labels

[Erik Joelsson]

We are currently experiencing an issue where GitLab returns 500 when we add or remove labels to a merge request. The label change still happens though, so to keep things running, I'm going to implement a temporary workaround to ignore the 500 result on these particular REST calls.

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Commit messages:
 - SKARA-1612

Changes: https://git.openjdk.org/skara/pull/1384/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1384&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1612
  Stats: 20 lines in 1 file changed: 16 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1384.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1384/head:pull/1384

PR: https://git.openjdk.org/skara/pull/1384