Gradle scripts for publishing to Maven Central shouldn't sign specific files

About a year ago, I deployed a Gradle project to Maven Central, which was made difficult by the signing requirement. I found a third-party guide that provided a very long snippet of buildscript to explicitly sign the POM (project manifest XML file) and various other files. After updating the project to Gradle 6, that didn't work anymore; the files that got signed were not the ones actually uploaded, so the signatures were invalid. Gradle 6 also introduced a new file that wasn't getting signed properly. After some poking around I discovered that signing specific files is not necessary when using the maven-publish plugin. The signing plugin can sign an entire publication as long as its configuration is written after the part of the buildscript that declares the publication:

signing {

    sign publishing.publications.getByName("mavenJava")

}

That change also made my check for duplicate signed files unnecessary.

A full working version can be found on GitHub.