Rollback nexus-staging-maven-plugin from 1.6.9 to 1.6.8

Revert "Merge branch 'dependabot/maven/org.sonatype.plugins-nexus-staging-maven-plugin-1.6.9' into 'master'"

This reverts merge request !682 (merged)

Reason https://issues.sonatype.org/browse/NEXUS-31214?focusedCommentId=1140935&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-1140935