[jdk21u-dev] RFR: 8350383: Test: add more test case for string compare (UL case)

[Goetz Lindenmaier]

I backport this test change as it also goes to 21.0.9-oracle

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Commit messages:
 - Backport c73fead5caea8008586b31a5009c64011637b8cc

Changes: https://git.openjdk.org/jdk21u-dev/pull/1790/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1790&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350383
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1790.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1790/head:pull/1790

PR: https://git.openjdk.org/jdk21u-dev/pull/1790