[jdk17u-dev] RFR: 8302109: Trivial fixes to btree tests

[Goetz Lindenmaier]

I backport this for parity with 17.0.11-oracle.

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Commit messages:
 - Backport 97d0c8720d46de8bd1620de975f6de3ba3eea560

Changes: https://git.openjdk.org/jdk17u-dev/pull/1974/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1974&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302109
  Stats: 9 lines in 4 files changed: 1 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1974.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1974/head:pull/1974

PR: https://git.openjdk.org/jdk17u-dev/pull/1974