[jdk21u-dev] RFR: 8321894: Bump update version for OpenJDK: 21.0.3

[Severin Gehwolf]

Required version bump to get `21.0.3` development going.

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Commit messages:
 - 8321894: Bump update version for OpenJDK: 21.0.3

Changes: https://git.openjdk.org/jdk21u-dev/pull/13/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=13&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321894
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/13.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/13/head:pull/13

PR: https://git.openjdk.org/jdk21u-dev/pull/13