Scala.js: Update the status of two tests.

They do not cause a StackOverflow error anymore, but they still do
not pass due to other reasons.

Author: sjrd

project/Build.scala

@@ -1104,10 +1104,10 @@ object Build {
             )).get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/library" ** (("*.scala": FileFilter)
-            -- "BigIntTest.scala" // StackOverflow in the compiler
+            -- "BigIntTest.scala" // Ambiguous reference because of new non-shadowing rule in Scala 3, pending update upstream
             -- "ObjectTest.scala" // compile errors
             -- "StackTraceTest.scala" // would require `npm install source-map-support`
-            -- "UnionTypeTest.scala" // requires a Scala 2 macro + StackOverflow in the compiler
+            -- "UnionTypeTest.scala" // requires a Scala 2 macro
             )).get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/niobuffer" ** "*.scala").get