[jdk8u-dev] RFR: 8330415: Update system property for Java SE specification maintenance version

[Justin Lu]

Please review this PR which is a backport of https://github.com/openjdk/jdk8u-ri/commit/bda97a28e0d0830b3c07b33482c4d6a99524af99.
This is a trivial increment of the `"java.specification.maintenance.version"` system property value from 5 to 6.
Associated GHA run: https://github.com/justin-curtis-lu/jdk8u-dev/actions/runs/9354657529.

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Commit messages:
 - 8330415: Update system property for Java SE specification maintenance version

Changes: https://git.openjdk.org/jdk8u-dev/pull/521/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=521&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330415
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/521.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/521/head:pull/521

PR: https://git.openjdk.org/jdk8u-dev/pull/521