Include headers in package data

This seemed unnecessary (under python3.12 and setuptools 73.0.1, while
on CI (python 3.7, and an undetermined setuptools version) headers were
not being bundled. Explicitly listing them should solve the issue
though.

Signed-off-by: Rodrigo Tobar <[email protected]>

setup.py

@@ -64,7 +64,7 @@
     classifiers=classifiers,
     packages=["crc32c"],
     package_dir={"": "src"},
-    package_data={"crc32c": ["*.pyi", "py.typed"]},
+    package_data={"crc32c": ["*.pyi", "py.typed", "ext/*.h"]},
     python_requires=">=3.7",
     ext_modules=[crcmod_ext],
     test_suite="test",