RFR: 8343551: Missing copyright header update in Charset-X-Coder.java.template

[Archie Cobbs]

Please review this trivial patch to fix a missed copyright header update in the fix for [JDK-8343484](https://bugs.openjdk.org/browse/JDK-8343551).

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Commit messages:
 - Update copyright header after JDK-8343484.

Changes: https://git.openjdk.org/jdk/pull/21882/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21882&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343551
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21882.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21882/head:pull/21882

PR: https://git.openjdk.org/jdk/pull/21882