RFR: Update BotSlackHandlerTest timeout

[Robin Westberg]

The timeout in combination with the default throttling can cause the test the fail.

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Commit messages:
 - Avoid timeout

Changes: https://git.openjdk.java.net/skara/pull/1007/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1007&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1007.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1007/head:pull/1007

PR: https://git.openjdk.java.net/skara/pull/1007