[jdk15u-dev] RFR: 8283443: Bump update version for OpenJDK: jdk-15.0.8

[Yuri Nesterenko]

Switch the the new (July) release in this release train.

-------------

Commit messages:
 - 8283443: Bump update version for OpenJDK: jdk-15.0.8

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/185/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=185&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283443
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/185.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/185/head:pull/185

PR: https://git.openjdk.java.net/jdk15u-dev/pull/185