[2.x] fix: Format Seq values consistently in multi-project builds (fixes #7339) (#8567)

When running commands like 'Test/definedTests' on multi-project builds,
the output was showing raw Vector(...) format instead of nicely formatted
per-item output.

Before:
  [info] svc / Test / definedTests
  [info]   Vector(Test FooSpec : ..., Test BarSpec : ..., ...)

After:
  [info] svc / Test / definedTests
  [info]   * Test FooSpec : ...
  [info]   * Test BarSpec : ...

The fix extends printSettings to check if values are Seq types in
the multi-project case and format each item on its own line with
a '* ' prefix, matching the single-project behavior.

main/src/main/scala/sbt/internal/Aggregation.scala

@@ -55,7 +55,17 @@ object Aggregation {
       case KeyValue(_, x: Seq[?]) :: Nil => print(x.mkString("* ", "\n* ", ""))
       case KeyValue(_, x) :: Nil         => print(x.toString)
       case _ =>
-        xs foreach (kv => print(display.show(kv.key) + "\n\t" + kv.value.toString))
+        xs foreach { kv =>
+          print(display.show(kv.key))
+          kv.value match {
+            case seq: Seq[?] if seq.nonEmpty =>
+              seq.foreach(item => print("\t* " + item.toString))
+            case seq: Seq[?] =>
+              print("\t(empty)")
+            case x =>
+              print("\t" + x.toString)
+          }
+        }
     }
 
   type Values[T] = Seq[KeyValue[T]]