RFR: 8297067: Update Gradle to 7.6

[Ambarish Rapte]

This upgrades gradle to 7.6, It is blocker for upgrading Boot JDK to 19.
gradle 7.3 does not support JDK 19.
Tested that, gradle 7.6 works with JDK 17, 18, 19.

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Commit messages:
 - jcheck fix
 - Notice
 - gradle-7.6

Changes: https://git.openjdk.org/jfx/pull/973/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=973&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297067
  Stats: 55 lines in 6 files changed: 36 ins; 1 del; 18 mod
  Patch: https://git.openjdk.org/jfx/pull/973.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/973/head:pull/973

PR: https://git.openjdk.org/jfx/pull/973