RFR: 8290049: Committers should be able to review for Shenandoah 8u

[Andrew John Hughes]

According to @rkennke, "it is sufficient to be a Committer in order to officially review Shenandoah PRs"

We should change the `jcheck` configuration to reflect this.

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Commit messages:
 - 8290049: Committers should be able to review for Shenandoah 8u

Changes: https://git.openjdk.org/shenandoah-jdk8u/pull/4/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk8u&pr=4&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290049
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk8u/pull/4.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk8u pull/4/head:pull/4

PR: https://git.openjdk.org/shenandoah-jdk8u/pull/4