RFR: Use a simpler way to detect legacy notifications

[Robin Westberg]

Hi all,

Please review this small change that uses a more robust way to detect if a commit in a PR has been served by the old
mailing list notifier.

Best regards,
Robin

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Commit messages:
 - Use a simpler way to detect when a legacy notification could have been issued

Changes: https://git.openjdk.java.net/skara/pull/611/files
 Webrev: https://webrevs.openjdk.java.net/skara/611/webrev.00
  Stats: 20 lines in 2 files changed: 4 ins; 8 del; 8 mod
  Patch: https://git.openjdk.java.net/skara/pull/611.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/611/head:pull/611

PR: https://git.openjdk.java.net/skara/pull/611