RFR: 1873: Possible notification race with tags

[Zhao Song]

As Erik said in the issue description, "If a new commit is integrated into a repository branch and quickly tagged, the notifier may miss updating the "Resolved In Build" field in the issue associated with that commit. This happens if the same RepositoryWorkItem instance handles both the tag and the commit, because it will handle the tag first, before a suitable backport has been created".

To solve this issue, we need to rearrange the order of handles of the tags and commits. 

I checked the logic in the two methods(**handleTags** and **handleRef**) and I couldn't find any problem would be introduced due to this change. But I could not guarantee that no problem would be found later.

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Commit messages:
 - SKARA-1873

Changes: https://git.openjdk.org/skara/pull/1507/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1507&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1873
  Stats: 85 lines in 2 files changed: 79 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1507.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1507/head:pull/1507

PR: https://git.openjdk.org/skara/pull/1507