Skip the sample app when publishing (#5)

The publish task evaluates `:sample-app`, which needs credentials/config files
that do not exist on a CI runner. Pass `-PskipSampleApp=true` as
android-for-googlemaps and android-for-arcgis already do.

Author: wf9a5m75

.github/workflows/publish-maven-central.yml

@@ -97,7 +97,7 @@ jobs:
           fi
 
           echo "  Will publish local version ${local_version} (remote='${remote_version}')."
-          ./gradlew --no-daemon publishAllPublicationsToCentralPortal
+          ./gradlew --no-daemon -PskipSampleApp=true publishAllPublicationsToCentralPortal
           gradle_exit=$?
           if [[ $gradle_exit -ne 0 ]]; then
             echo "Gradle publish failed with exit code $gradle_exit"