fix off by one error when printing line of previously declared symbol

Author: Jendrik Wenke

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

@@ -2088,7 +2088,7 @@ object messages {
         case Signature.ParamMatch => "\nOverloads with equal parameter types but different return types are not allowed."
         case Signature.FullMatch => "\nThe definitions have the same signature after erasure."
       }
-      hl"${decl.showLocated} is already defined as ${previousSymbol.showDcl} in line ${previousSymbol.pos.line}." + details
+      hl"${decl.showLocated} is already defined as ${previousSymbol.showDcl} in line ${previousSymbol.pos.line + 1}." + details
     }
     val explanation = ""
   }

tests/neg/doubleDefinition.scala

@@ -9,14 +9,7 @@ class Test1 {
 
 
 class Test2 {
-
-
-
-	def foo(
-		       x: List[A]
-	       ): Function1[A,
-		A] =
-		???
+	def foo(x: List[A]): Function1[A, A] = ???
 	def foo(x: List[B]): Function1[B, B] = ??? // error: same jvm signature
 	// scalac calls this "have same type after erasure"
 }