RFR: 8344967: Some tests in TestFill do not use the test parameter

[Per Minborg]

This trivial PR proposes to use the parameter length for two tests as originally intended.

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Commit messages:
 - Fix parameter use

Changes: https://git.openjdk.org/jdk/pull/22413/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22413&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344967
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22413.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22413/head:pull/22413

PR: https://git.openjdk.org/jdk/pull/22413