Avoid using `Task.project` at task execution time

Accessing `Task.project` at execution time is being deprecated in Gradle 8.12, and will be forbidden in a future Gradle release.

https://github.com/nebula-plugins/gradle-dependency-lock-plugin/blob/7cf2415f6b262e1f7a4bc3e661c68e26a1cd8ff1/src/main/groovy/nebula/plugin/dependencylock/tasks/GenerateLockTask.groovy#L76

See: https://github.com/gradle/gradle/issues/30860