Integrated: Cache repeated calls for GitLab labels

[Robin Westberg]

Hi all,

Please review this small change that caches repeated calls to GitLab PR labels, similar to how GitHub does.

Best regards,
Robin

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Commit messages:
 - Cache repeated calls for GitLab labels

Changes: https://git.openjdk.java.net/skara/pull/772/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=772&range=00
  Stats: 16 lines in 1 file changed: 11 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/772.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/772/head:pull/772

PR: https://git.openjdk.java.net/skara/pull/772