[jdk21u-dev] RFR: 8326773: Bump update version for OpenJDK: jdk-21.0.4

[Severin Gehwolf]

Development for `21.0.4` starts Wednesday, Feb 28. This is the needed version bump.

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Commit messages:
 - 8326773: Bump update version for OpenJDK: 21.0.4

Changes: https://git.openjdk.org/jdk21u-dev/pull/295/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=295&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326773
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/295.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/295/head:pull/295

PR: https://git.openjdk.org/jdk21u-dev/pull/295