Use project instead of this@Build_gradle

The Kotlin 2 compiler in Gradle 9 no longer resolves the label this@Build_gradle, which fails with Unresolved label. On Gradle 8.14 the label is the script object rather than the Project, so it only offers the script API, such as file(..) and logger, and those calls move to project. A member the script declares itself, a label inside subprojects, allprojects, project(..) or configure(..) where project is a different project, and a bare label are left alone. See the Gradle upgrade guide for more information.