ci: skip central-publishing upload during internal Exit Gate CI validation builds (#405)

Change-Id: I945fa5a4a260ac8837f134c97e7fb4e2799a81b4

Co-authored-by: Anshul Patni <anshulpatni@google.com>

Author: AnshulPatni

.kokoro/build.sh

@@ -106,6 +106,8 @@ mvn clean deploy -B \
   -P sonatype-oss-release \
   --settings=../settings.xml \
   -DaltDeploymentRepository=exit-gate-ar::https://us-maven.pkg.dev/oss-exit-gate-prod/ff-releases--mavencentral \
+  -DskipPublishing=true \
+  -Dcentral.skipPublishing=true \
   -Dgpg.executable=gpg \
   -Dgpg.passphrase="${GPG_PASSPHRASE}" \
   -Dgpg.homedir="${GNUPGHOME}"