Jars are overwritten during release with -Ppublishing

+cc pabloem boyuanz lukecwik

Few jars (*-shaded.jar and *-tests.jar) are missing if I run `./gradlew -Ppublishing :publishToMavenLocal`.

However, I can get them through assemble and shadowJar. For example, `./gradlew :beam-sdks-java-core:assemble :beam-sdks-java-core:shadowJar`.

This could be the reason why we can't run parallel build during release.