[jdk21u] RFR: 8313312: Add missing classpath exception copyright header

[Roger Riggs]

The same copyright updates are needed in jdk21u.

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Commit messages:
 - Backport 53ca75b18ea419d469758475fac8352bf915b484

Changes: https://git.openjdk.org/jdk21u/pull/71/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=71&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313312
  Stats: 48 lines in 16 files changed: 32 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk21u/pull/71.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/71/head:pull/71

PR: https://git.openjdk.org/jdk21u/pull/71