RFR: 1663: Mark integrated Pull Requests as properly merged in their repositories [v8]

[Julian Waters]

> WIP

Julian Waters has updated the pull request incrementally with one additional commit since the last revision:

  Implement merging for GitLab

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1409/files
  - new: https://git.openjdk.org/skara/pull/1409/files/673e95d9..d90f9042

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1409&range=07
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1409&range=06-07

  Stats: 11 lines in 1 file changed: 4 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/skara/pull/1409.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1409/head:pull/1409

PR: https://git.openjdk.org/skara/pull/1409