Don't import blinka _bleio during docs build

Author: dhalbert

docs/conf.py

@@ -21,7 +21,7 @@
 # Uncomment the below if you use native CircuitPython modules such as
 # digitalio, micropython and busio. List the modules you use. Without it, the
 # autodoc module docs will fail to generate with a warning.
-autodoc_mock_imports = ["board", "microcontroller"]
+autodoc_mock_imports = ["_bleio", "board", "microcontroller"]
 autodoc_member_order = "bysource"
 add_module_names = False