RFR: 8357842: PandocFilter misses copyright header

[Magnus Ihse Bursie]

`make/jdk/src/classes/build/tools/pandocfilter/PandocFilter.java` misses a copyright header.

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Commit messages:
 - 8357842: PandocFilter misses copyright header

Changes: https://git.openjdk.org/jdk/pull/25463/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25463&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357842
  Stats: 23 lines in 1 file changed: 23 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25463.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25463/head:pull/25463

PR: https://git.openjdk.org/jdk/pull/25463