RFR: 998: Backport fails for jdk15u-dev

[Erik Helin]

Hi all,

please review this patch that fixes the REST endpoint used by `GitHubRepository.canPush`.

Thanks,
Erik

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Commit messages:
 - skara-998

Changes: https://git.openjdk.java.net/skara/pull/1140/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1140&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-998
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1140.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1140/head:pull/1140

PR: https://git.openjdk.java.net/skara/pull/1140