RFR: 8321123: [Shenandoah/JDK21] Fix repo permissions [v3]

[Roman Kennke]

> The Shenandoah/JDK21u repo has the wrong permissons: it inherits permissions from jdk-updates, but should use permission from she Shenandoah project instead.

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Allow committers to review

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/3/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/3/files/32f68445..0a3b6306

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=3&range=02
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=3&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/3.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/3/head:pull/3

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/3