[jdk21u-dev] RFR: 8352879: TestPeriod.java and TestGetContentType.java run wrong test class

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle.

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Commit messages:
 - Backport b9d7a75adee8a96cf47bbe73e3009102ceda9589

Changes: https://git.openjdk.org/jdk21u-dev/pull/1954/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1954&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352879
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1954.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1954/head:pull/1954

PR: https://git.openjdk.org/jdk21u-dev/pull/1954