RFR: 8531: UI tests fail on Mac OS

[Marcus Hirt]

Fixing uitests on Mac OS. Now they pass on my M1.

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Commit messages:
 - 8531: Fixing uitests on Mac OS

Changes: https://git.openjdk.org/jmc/pull/707/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=707&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8531
  Stats: 536 lines in 19 files changed: 448 ins; 7 del; 81 mod
  Patch: https://git.openjdk.org/jmc/pull/707.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/707/head:pull/707

PR: https://git.openjdk.org/jmc/pull/707