Make more tests run on Windows (#8446)

* Remove worker Wait() call due to SIGCHLD being ignored

* Port _pid_alive to Windows

* Show PID as well as TID in glog

* Update TensorFlow version for Python 3.8 on Windows

* Handle missing Pillow on Windows

* Work around dm-tree PermissionError on Windows

* Fix some lint errors on Windows with Python 3.8

* Simplify torch requirements

* Quiet git clean

* Handle finalizer issues

* Exit with the signal number

* Get rid of wget

* Fix some Windows compatibility issues with tests

Co-authored-by: Mehrdad <noreply@github.com>

python/ray/tests/test_actor.py

@@ -358,7 +358,7 @@ def test_decorator_args(ray_start_regular):
     with pytest.raises(Exception):
 
         @ray.remote(invalid_kwarg=0)  # noqa: F811
-        class Actor:
+        class Actor:  # noqa: F811
             def __init__(self):
                 pass
 
@@ -366,25 +366,25 @@ def test_decorator_args(ray_start_regular):
     with pytest.raises(Exception):
 
         @ray.remote(num_cpus=0, invalid_kwarg=0)  # noqa: F811
-        class Actor:
+        class Actor:  # noqa: F811
             def __init__(self):
                 pass
 
     # This is a valid way of using the decorator.
     @ray.remote(num_cpus=1)  # noqa: F811
-    class Actor:
+    class Actor:  # noqa: F811
         def __init__(self):
             pass
 
     # This is a valid way of using the decorator.
     @ray.remote(num_gpus=1)  # noqa: F811
-    class Actor:
+    class Actor:  # noqa: F811
         def __init__(self):
             pass
 
     # This is a valid way of using the decorator.
     @ray.remote(num_cpus=1, num_gpus=1)  # noqa: F811
-    class Actor:
+    class Actor:  # noqa: F811
         def __init__(self):
             pass