[2.x] test: Enable run/fork-loader scripted test (#9199)

sbt-app/src/sbt-test/run/fork-loader/build.sbt

@@ -6,5 +6,6 @@ lazy val root = (project in file("."))
   .settings(
     name := "forked-test",
     organization := "org.example",
+    Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Raw,
     libraryDependencies += scalacheck % Test
   )

sbt-app/src/sbt-test/run/fork-loader/test

@@ -1,6 +1,6 @@
 # This test verifies that the forked code is loaded in the application class loader.
 -> run
--> test
+-> testFull
 > set fork := true
 > run
-> test
+> testFull