Update error message

Co-authored-by: Nicolas Stucki <nicolas.stucki@gmail.com>

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -1323,7 +1323,7 @@ class VarArgsParamCannotBeGiven(isGiven: Boolean)(using Context)
 extends SyntaxMsg(VarArgsParamCannotBeGivenID) {
   def msg(using Context) = i"repeated parameters are not allowed in a ${if isGiven then "using" else "implicit"} clause"
   def explain(using Context) =
-    "It is not possible to define a given with a repeated parameter type."
+    "It is not possible to define a given with a repeated parameter type. This hypothetical given parameter could always be satisfied by providing 0 arguments, which defeats the purpose of a given argument."
 }