RFR: 8345876: Update nativeAddAtIndex comment to match the code

[Saagar Jha]

8345876: Update nativeAddAtIndex comment to match the code

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Commit messages:
 - Update nativeAddAtIndex comment to match the code

Changes: https://git.openjdk.org/jdk/pull/22627/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22627&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345876
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22627.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22627/head:pull/22627

PR: https://git.openjdk.org/jdk/pull/22627