RFR: 8323730: Tweak TestZAllocationStallEvent.java to allocate smaller objects

[Stefan Karlsson]

This is a minor tweak to TestZAllocationStallEvent.java in an attempt to lower the risk of hitting OOME while provoking allocation stalls.

Tested by running tier5, where the test has been found to very intermittently cause problems.

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

Commit messages:
 - 8323730: Tweak TestZAllocationStallEvent.java to allocate smaller objects

Changes: https://git.openjdk.org/jdk/pull/17426/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17426&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323730
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17426.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17426/head:pull/17426

PR: https://git.openjdk.org/jdk/pull/17426