RFR: 8268424: JFR tests fail due to GC cause 'G1 Preventive Collection' not in the valid causes after JDK-8257774

[Jie Fu]

Hi all, 

A new gc cause called 'G1 Preventive Collection' was added in JDK-8257774.
So the following two jfr tests should also be updated to fix the test failures.


jdk/jfr/event/gc/collection/TestGCCauseWithG1ConcurrentMark.java
jdk/jfr/event/gc/collection/TestGCCauseWithG1FullCollection.java


Thanks.
Best regards,
Jie

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Commit messages:
 - 8268424: JFR tests fail due to GC cause 'G1 Preventive Collection' not in the valid causes after JDK-8257774

Changes: https://git.openjdk.java.net/jdk/pull/4422/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4422&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268424
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4422.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4422/head:pull/4422

PR: https://git.openjdk.java.net/jdk/pull/4422