Address some build warnings and cleanup (#1412)

i18n/build.gradle.kts

@@ -1,6 +1,6 @@
 import mihon.buildlogic.generatedBuildDir
 import mihon.buildlogic.tasks.getLocalesConfigTask
-import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
 
 plugins {
     id("mihon.library")
@@ -20,6 +20,11 @@ kotlin {
             }
         }
     }
+
+    @OptIn(ExperimentalKotlinGradlePluginApi::class)
+    compilerOptions {
+        freeCompilerArgs.add("-Xexpect-actual-classes")
+    }
 }
 
 val generatedAndroidResourceDir = generatedBuildDir.resolve("android/res")
@@ -49,10 +54,4 @@ tasks {
     preBuild {
         dependsOn(localesConfigTask)
     }
-
-    withType<KotlinCompile> {
-        compilerOptions.freeCompilerArgs.addAll(
-            "-Xexpect-actual-classes",
-        )
-    }
 }