Suppress "extension method will never be selected" for overrides

compiler/test/dotc/pos-test-pickling.blacklist

@@ -30,6 +30,7 @@ strict-pattern-bindings-3.0-migration.scala
 i17186b.scala
 i11982a.scala
 i17255
+i17735.scala
 
 # Tree is huge and blows stack for printing Text
 i7034.scala

tests/pos-special/fatal-warnings/i17735.scala → tests/pos/i17735.scala

@@ -1,4 +1,4 @@
-//> using options -Wvalue-discard
+//> using options -Xfatal-warnings -Wvalue-discard
 
 import scala.collection.mutable
 import scala.annotation.nowarn
@@ -21,4 +21,4 @@ object Foo:
       // here @nowarn is effective without -Wfatal-warnings (i.e. no warning)
       // But with -Wfatal-warnings we get an error
       messageBuilder.append("\n").append(s): @nowarn("msg=discarded non-Unit value*")
-    messageBuilder.result()
+    messageBuilder.result()

tests/pos-special/fatal-warnings/i17735a.scala → tests/pos/i17735a.scala

@@ -1,4 +1,4 @@
-//> using options -Wvalue-discard -Wconf:msg=non-Unit:s
+//> using options -Xfatal-warnings -Wvalue-discard -Wconf:msg=non-Unit:s
 
 import scala.collection.mutable
 import scala.annotation.nowarn

tests/pos-special/fatal-warnings/i17741.scala → tests/pos/i17741.scala

@@ -1,4 +1,4 @@
-//> using options -Wnonunit-statement
+//> using options -Xfatal-warnings -Wnonunit-statement
 
 class Node()
 class Elem(
@@ -29,4 +29,4 @@ object Main {
       )
     }
   }: @annotation.nowarn()
-}
+}

tests/pos-special/fatal-warnings/nowarnannot.scala → tests/pos/nowarnannot.scala

@@ -1,3 +1,5 @@
+//> using options -Xfatal-warnings -Wvalue-discard
+
 case class F(i: Int)
 
 object Main {