[jdk11u-dev] RFR: 8277796: Bump update version for OpenJDK: jdk-11.0.15

[Goetz Lindenmaier]

Necessary change to start update 15 of jdk11u.

Will push after tagging 11.0.15+0 next Tuesday.

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Commit messages:
 - 8277796: Bump update version for OpenJDK: jdk-11.0.15

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/662/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=662&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277796
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/662.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/662/head:pull/662

PR: https://git.openjdk.java.net/jdk11u-dev/pull/662