RFR: jdk21: Unit test updated to pass with JDK 21 and above.

[Leonid Kuskov]

Fixed issue caused by switching the build to JDK 21.

-------------

Commit messages:
 - jdk21: Unit test updated to pass with JDK 21 and above.

Changes: https://git.openjdk.org/asmtools/pull/75/files
  Webrev: https://webrevs.openjdk.org/?repo=asmtools&pr=75&range=00
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/asmtools/pull/75.diff
  Fetch: git fetch https://git.openjdk.org/asmtools.git pull/75/head:pull/75

PR: https://git.openjdk.org/asmtools/pull/75