Fix the project isolation issues

With the new project isolation feature in Gradle there are restrictions
on what you can access on a `Project` instance for another module.

common/validation/src/main/kotlin/com/github/triplet/gradle/common/validation/Validation.kt

@@ -10,15 +10,15 @@ import org.gradle.api.logging.Logger
 import org.gradle.kotlin.dsl.apply
 import org.gradle.kotlin.dsl.findByType
 import org.gradle.kotlin.dsl.withType
+import org.gradle.util.GradleVersion
 
 /**
  * Validates required dependencies. If GPP can't run in the current context, an error will be
  * thrown.
  */
 fun Project.validateRuntime() {
-    rootProject.plugins.apply(RuntimeValidationPlugin::class)
-
-    project.plugins.withType<AppPlugin> {
+    GradleRuntimeValidator(GradleVersion.current(), MIN_GRADLE_VERSION).validate()
+    plugins.withType<AppPlugin> {
         val agpPluginVersion = extensions.findByType<ApplicationAndroidComponentsExtension>()?.pluginVersion
         AgpRuntimeValidator(agpPluginVersion, MIN_AGP_VERSION).validate()
     }

play/plugin/src/main/kotlin/com/github/triplet/gradle/play/PlayPublisherPlugin.kt

@@ -97,7 +97,7 @@ internal abstract class PlayPublisherPlugin @Inject constructor(
     }
 
     private fun applyInternal(project: Project) {
-        val executionDir = project.rootProject.layout.projectDirectory
+        val executionDir = project.rootDir
         val cliOptionsExtension = project.objects.newInstance<CliPlayPublisherExtension>()
         val bootstrapOptionsHolder = BootstrapOptions.Holder()