[doc] Use list[int] instead of List[int] (etc.) in a few more places (GH-22524)



This changes a few occurrences left behind by #22340.

Automerge-Triggered-By: @gvanrossum
diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst
index 6e74af0..e706f7f 100644
--- a/Doc/library/dataclasses.rst
+++ b/Doc/library/dataclasses.rst
@@ -188,7 +188,7 @@
 
      @dataclass
      class C:
-         mylist: List[int] = field(default_factory=list)
+         mylist: list[int] = field(default_factory=list)
 
      c = C()
      c.mylist += [1, 2, 3]
@@ -301,7 +301,7 @@
 
      @dataclass
      class C:
-          mylist: List[Point]
+          mylist: list[Point]
 
      p = Point(10, 20)
      assert asdict(p) == {'x': 10, 'y': 20}