RFR: 2322: Notify when PR is ready for sponsor in GitLab

[Zhao Song]

In [SKARA-2302](https://bugs.openjdk.org/browse/SKARA-2302), I tried to let the bot send an email notification about the "pr is ready for sponsor" comment.
But today, I noticed that it only works in GitHub not works in GitLab.

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Commit messages:
 - SKARA-2322

Changes: https://git.openjdk.org/skara/pull/1674/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1674&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2322
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1674.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1674/head:pull/1674

PR: https://git.openjdk.org/skara/pull/1674