Set docker VCS_REF back to a 7 char hash (hyperledger#7551)

Signed-off-by: Matilda Clerke <[email protected]>

build.gradle

@@ -819,7 +819,7 @@ task distDocker {
         dockerPlatform = "--platform ${project.getProperty('docker-platform')}"
         println "Building for platform ${project.getProperty('docker-platform')}"
       }
-      def gitDetails = getGitCommitDetails()
+      def gitDetails = getGitCommitDetails(7)
       executable shell
       workingDir dockerBuildDir
       args "-c", "docker build ${dockerPlatform} --build-arg BUILD_DATE=${buildTime()} --build-arg VERSION=${dockerBuildVersion} --build-arg VCS_REF=${gitDetails.hash} -t ${image} ."