RFR: 8276995: Bug in jdk.jfr.event.gc.collection.TestSystemGC

[Robert Toyonaga]

Just a tiny test case fix. The test was previously checking the wrong events.

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Commit messages:
 - trivial testcase fix

Changes: https://git.openjdk.org/jdk/pull/23445/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23445&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8276995
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23445.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23445/head:pull/23445

PR: https://git.openjdk.org/jdk/pull/23445