RFR: 8325001: Typo in the javadocs for the Arena::ofShared method

[Per Minborg]

This PR fixes a typo in the documentation for the `Arena::ofShared`.

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Commit messages:
 - Fix typo

Changes: https://git.openjdk.org/jdk/pull/17653/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17653&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325001
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17653.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17653/head:pull/17653

PR: https://git.openjdk.org/jdk/pull/17653