Fix main: remove empty parentheses when rewriting implicits to givens (#23339)

Author: jchyb

compiler/src/dotty/tools/dotc/typer/Migrations.scala

@@ -202,6 +202,10 @@ trait Migrations:
         patch(
           Span(ddef.mods.mods.last.span.end + 1, ddef.namePos.span.start), "given "
         )
+        // remove empty parentheses
+        patch(
+          Span(ddef.namePos.span.end, ddef.tpt.span.start), ": "
+        )
         ddef.tpt match
           case refinedType: untpd.RefinedTypeTree =>
             patch(refinedType.span.startPos, "(")

tests/rewrites/implicit-to-given.check

@@ -17,7 +17,7 @@ object Def:
   val application = applicationTest(using 0)
   val implicitArg: Int => Unit = (implicit a => applicationTest) // should not change
 
-  given refined(): (A {type B = Int}) = ???
+  given refined: (A {type B = Int}) = ???
 
   class EmptyParamListClass()(using a: Int)
   def emptyParamListTest() = new EmptyParamListClass()(using 0)