Make scalatest-overload-3.7.scala a warn test

Author: EugeneFlesselle

tests/warn/scalatest-overload-3.7.check

@@ -0,0 +1,13 @@
+-- Warning: tests/warn/scalatest-overload-3.7.scala:22:18 --------------------------------------------------------------
+22 |    "hello world" should endWith ("world") // warn: overloading resolution change
+   |                  ^^^^^^
+   |              Overloading resolution for arguments (("hello world" : String))(EndWithWord) between alternatives
+   |               [T](leftSideValue: T)(word: EndWithWord)(using x$3: T <:< String): Unit
+   |               [T](leftSideValue: T)(word: StartWithWord)(using x$3: T <:< String): Unit
+   |               (leftSideString: String)(body: TestBody2): Unit
+   |               (leftSideString: String)(body: TestBody1): Unit
+   |              will change.
+   |              Current choice           : [T](leftSideValue: T)(word: EndWithWord)(using x$3: T <:< String): Unit
+   |              New choice from Scala 3.7: none
+   |
+   |              where:    T is a type variable with constraint >: ("hello world" : String)

tests/neg/scalatest-overload-3.7.scala renamed to tests/warn/scalatest-overload-3.7.scala

@@ -1,4 +1,4 @@
-import scala.language.`3.8`
+import scala.language.`3.7`
 
 class TestBody1
 class TestBody2
@@ -19,4 +19,4 @@ class Matchers:
 
 class Test extends Matchers:
   def test(): Unit =
-    "hello world" should endWith ("world") // error
+    "hello world" should endWith ("world") // warn: overloading resolution change