RFR: 8334332: Run TestIOException.java with root user fails

[SendaoYan]

Hi all,
  Test `test/langtools/jdk/javadoc/doclet/testIOException/TestIOException.java` run fails with root user privileged. I think it's necessary to skip this testcase when user is root.
  The change has been verified, only change the testcase, no risk.

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Commit messages:
 - 8334332: TestIOException.java fails run with root user

Changes: https://git.openjdk.org/jdk/pull/19731/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19731&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334332
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19731.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19731/head:pull/19731

PR: https://git.openjdk.org/jdk/pull/19731