Change default value for failOnUncoveredSourceFiles to true

As uncovered source files are never included in the package which is almost never intended the default value of failOnUncoveredSourceFiles (https://jackrabbit.apache.org/filevault-package-maven-plugin/package-mojo.html#failOnUncoveredSourceFiles) should be changed to true.
One example where the default behaviour leads to issues is tracked at https://github.com/Adobe-Consulting-Services/acs-aem-commons/issues/2826.