Remove the Maven 3.9 pin from the release workflow after 14.3.0 #870

The release job in .github/workflows/release.yml downloads Maven 3.9.16 instead of using the runner's Maven. Under Maven 3.10, central-publishing-maven-plugin 0.11.0 adds maven-metadata-local.xml and _remote.repositories to the bundle, and Central rejects it:

Bundle has content that does NOT have a .pom file

Plugin 0.12.0 fixes this (sonatype-nexus-community/central-publishing-maven-plugin#1), and #848 bumps to it. I built the release bundle locally with a throwaway release version:

• Maven 3.10.0 + 0.11.0: both files are in central-bundle.zip
• Maven 3.10.0 + 0.12.0: neither is
• Maven 3.9.16 + 0.12.0: neither is

I haven't checked whether Central accepts the bundle, since only a real release can show that. So the pin stays for 14.3.0, since it works with either plugin version. Once 14.3.0 publishes with 0.12.0, the "Setup Maven 3.9" step can go.