Don't propagae mandatoryScalacOptions to tests, too

Needed to add a MiMa exclusion, which should be safe in this case.

build.mill

@@ -522,6 +522,11 @@ trait MillStableScalaModule extends MillPublishScalaModule with Mima {
     ),
     ProblemFilter.exclude[InheritedNewAbstractMethodProblem](
       "mill.main.MainModule.mill$define$BaseModule0$_setter_$evalWatchedValues_="
+    ),
+
+    // https://github.com/com-lihaoyi/mill/pull/3503
+    ProblemFilter.exclude[ReversedMissingMethodProblem](
+      "mill.scalalib.ScalaModule#ScalaTests.mill$scalalib$ScalaModule$ScalaTests$$super$mandatoryScalacOptions"
     )
   )
   def mimaPreviousVersions: T[Seq[String]] = Settings.mimaBaseVersions
@@ -875,7 +880,6 @@ object dist extends MillPublishJavaModule {
   }
 }
 
-
 /**
  * Build and install Mill locally.
  *

scalalib/src/mill/scalalib/ScalaModule.scala

@@ -34,7 +34,7 @@ trait ScalaModule extends JavaModule with TestModule.ScalaModuleBase { outer =>
     override def scalacPluginIvyDeps: Target[Agg[Dep]] = outer.scalacPluginIvyDeps()
     override def scalacPluginClasspath: Target[Agg[PathRef]] = outer.scalacPluginClasspath()
     override def scalacOptions: Target[Seq[String]] = outer.scalacOptions()
-    override def mandatoryScalacOptions: Target[Seq[String]] = outer.mandatoryScalacOptions()
+    override def mandatoryScalacOptions: Target[Seq[String]] = T{ super.mandatoryScalacOptions() }
   }
 
   /**