Move parsing unary_!_= test

Author: nicolasstucki

tests/neg-custom-args/fatal-warnings/i9241.scala

@@ -16,7 +16,6 @@ final class Baz private (val x: Int) extends AnyVal {
   def unary_- : Baz = ???
   def unary_+[T] : Baz = ???
   def unary_!() : Baz = ??? // error
-  def `unary_!_=`() : Baz = ??? // ok
   def unary_~(using Int) : Baz = ???
 }
 

tests/pos/unary-eq.scala

@@ -0,0 +1,6 @@
+final class Baz private (val x: Int) extends AnyVal {
+  def `unary_!_=`() : Baz = ??? // parses ok, but will not be usable
+  def `unary_~_=`() : Baz = ??? // parses ok, but will not be usable
+  def `unary_+_=`() : Baz = ??? // parses ok, but will not be usable
+  def `unary_-_=`() : Baz = ??? // parses ok, but will not be usable
+}