Avoid redundant type test for irrefutable @unchecked patterns

Fixes #14896

Author: odersky

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

@@ -1378,7 +1378,7 @@ trait Applications extends Compatibility {
         val unapplyPatterns = bunchedArgs.lazyZip(argTypes) map (typed(_, _))
         val result = assignType(cpy.UnApply(tree)(unapplyFn, unapplyImplicits(unapplyApp), unapplyPatterns), ownType)
         unapp.println(s"unapply patterns = $unapplyPatterns")
-        if ((ownType eq selType) || ownType.isError) result
+        if (ownType.stripped eq selType.stripped) || ownType.isError then result
         else tryWithTypeTest(Typed(result, TypeTree(ownType)), selType)
       case tp =>
         val unapplyErr = if (tp.isError) unapplyFn else notAnExtractor(unapplyFn)

tests/pos/i14896.scala

@@ -0,0 +1,2 @@
+object Ex  { def unapply(p: Any): Option[_ <: Int] = null }
+object Foo { val Ex(_) = null: @unchecked }