RFR: JDK-8325255 jdk.internal.util.ReferencedKeySet::add using wrong test

[Jim Laskey]

Currently, add is returning intern(e) == null which will always be false. The correct test is intern(e) == e , that is, true when element is newly added.

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Commit messages:
 - Correct test

Changes: https://git.openjdk.org/jdk/pull/17732/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17732&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325255
  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17732.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17732/head:pull/17732

PR: https://git.openjdk.org/jdk/pull/17732