testlib: fix Pillow type annotations

Pillow upstream added a `py.typed` file in their last release, which is
causing us problems because:

  - we `from PIL import Image`, which kinda looks like the class `Image`
    in the `PIL` module, but is actually a submodule.  In particular,
    `PIL.Image.open()` is not a static method, but a function call, and
    it doesn't return `PIL.Image`, but rather `PIL.Image.Image`.  Fix a
    couple of annotations.

  - our hacks for setting `Image = None` if the import is missing are no
    longer working (since the import now has a better type than `Any`).
    Let's make the import unconditional.  `dnf install python3-pillow`.

  - several methods are unannotated in the upstream code, leading to
    warnings about "untyped call from typed code".  We use an #ignore
    for those; cf. python-pillow/Pillow#8029

pyproject.toml

@@ -25,7 +25,6 @@ module = [
     "machine.*",
     "task.*",
     "testvm",
-    "PIL",
 
     # run with bots checked out but its dependencies missing
     "libvirt",

test/common/testlib.py

@@ -42,11 +42,7 @@
 from lcov import write_lcov
 from lib.constants import OSTREE_IMAGES
 from machine import testvm
-
-try:
-    from PIL import Image
-except ImportError:
-    Image = None
+from PIL import Image
 
 _T = TypeVar('_T')
 _FT = TypeVar("_FT", bound=Callable[..., Any])
@@ -1203,12 +1199,13 @@ def ignorable_coord(x: int, y: int) -> bool:
             def ignorable_change(a: tuple[int, int, int], b: tuple[int, int, int]) -> bool:
                 return abs(a[0] - b[0]) <= 2 and abs(a[1] - b[1]) <= 2 and abs(a[2] - b[2]) <= 2
 
-            def img_eq(ref: Image, now: Image, delta: Image) -> bool:
+            def img_eq(ref: Image.Image, now: Image.Image, delta: Image.Image) -> bool:
                 # This is slow but exactly what we want.
                 # ImageMath might be able to speed this up.
-                data_ref = ref.load()
-                data_now = now.load()
-                data_delta = delta.load()
+                # no-untyped-call: see https://github.com/python-pillow/Pillow/issues/8029
+                data_ref = ref.load()  # type: ignore[no-untyped-call]
+                data_now = now.load()  # type: ignore[no-untyped-call]
+                data_delta = delta.load()  # type: ignore[no-untyped-call]
                 result = True
                 count = 0
                 width, height = delta.size
@@ -1233,7 +1230,7 @@ def img_eq(ref: Image, now: Image, delta: Image) -> bool:
                     # Preserve alpha channel so that the 'now'
                     # image can be used as the new reference image
                     # without further changes
-                    img_now.putalpha(img_ref.getchannel("A"))
+                    img_now.putalpha(img_ref.getchannel("A"))  # type: ignore[no-untyped-call]
                 img_now.save(filename)
                 attach(filename, move=True)
                 ref_filename_for_attach = base + "-reference.png"