Enable strict validation on CI (#467)

publish.gradle

@@ -13,4 +13,8 @@ publishing {
 
 apiValidation {
 	klib.enabled = true
+
+	// We run API checks on a Mac where all possible Kotlin targets are available.
+	// Setting this to true will allow us to catch when targets are removed.
+	klib.strictValidation = System.getenv("CI") == "true"
 }