BLD: Build PyPy 3.9 wheels. (#23023)

NumPy is dropping Python 3.8 for the 1.25.x release cycle. This updates
PyPy to 3.9 in order to be consistant with that.

Co-authored-by: Matti Picus <matti.picus@gmail.com>

.github/workflows/wheels.yml

@@ -78,10 +78,7 @@ jobs:
           - [macos-12, macosx_*]
           - [windows-2019, win_amd64]
           - [windows-2019, win32]
-        # TODO: uncomment PyPy 3.9 builds once PyPy
-        # re-releases a new minor version
-        # NOTE: This needs a bump of cibuildwheel version, also, once that happens.
-        python: ["cp39", "cp310", "cp311", "pp38"]  #, "pp39"]
+        python: ["cp39", "cp310", "cp311", "pp39"]
         exclude:
           # Don't build PyPy 32-bit windows
           - buildplat: [windows-2019, win32]