RFR: Fix the TestBot concurrency improvement

[Robin Westberg]

The fix to make the test bot more concurrent requires this additional fix in order to not interfere with other
scheduled tasks.

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Commit messages:
 - No concurrency improvements without this

Changes: https://git.openjdk.java.net/skara/pull/853/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=853&range=00
  Stats: 14 lines in 1 file changed: 13 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/853.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/853/head:pull/853

PR: https://git.openjdk.java.net/skara/pull/853