ci: fix deploy to maven central

[nicklasl]

Correct references

The maven plugin to deploy artefacts uses the repos defined in distributionManagement when uploading. These repos require username and passwords set as part of some place.

The actions/setup-java@v3 will setup a file /home/runner/.m2/settings.xml for us with the contents:

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 https://maven.apache.org/xsd/settings-1.0.0.xsd">
  <servers>
    <server>
      <id>ossrh</id>
      <username>${env.MAVEN_USERNAME}</username>
      <password>${env.MAVEN_PASSWORD}</password>
    </server>
    <server>
      <id>gpg.passphrase</id>
      <passphrase>${env.GPG_PASS}</passphrase>
    </server>
  </servers>
</settings>

The xml file references the environment variables MAVEN_USERNAME, MAVEN_PASSWORD and GPG_PASS which are set as environment variables in the Deploy with Maven step with the values from Github secrets.