Conditionally disable :example-frontend-js for snapshot train

It doesn't work properly with new JS IR BE because it depends on a really old plugin version
diff --git a/build.gradle b/build.gradle
index b6d0483..87aac2a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -134,6 +134,10 @@
 apply plugin: "binary-compatibility-validator"
 apiValidation {
     ignoredProjects += unpublished + ["kotlinx-coroutines-bom"]
+    if (build_snapshot_train) {
+        ignoredProjects.remove("site")
+        ignoredProjects.remove("example-frontend-js")
+    }
     ignoredPackages += "kotlinx.coroutines.internal"
 }
 
@@ -305,4 +309,4 @@
     moduleRoots = [".", "integration", "reactive", "ui"]
 }
 
-knitPrepare.dependsOn getTasksByName("dokka", true)
\ No newline at end of file
+knitPrepare.dependsOn getTasksByName("dokka", true)