RFR: 8372120: Add missing sound keyword to MIDI tests

[Alexander Zuev]

Add missing keyword to the tests where it is required but missing.

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Commit messages:
 - 8372120: Add missing sound keyword to MIDI tests

Changes: https://git.openjdk.org/jdk/pull/28382/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28382&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372120
  Stats: 5 lines in 5 files changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28382.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28382/head:pull/28382

PR: https://git.openjdk.org/jdk/pull/28382