examples: Mark asm, pio, etc. as noqa: F821 (undefined-name).

These files all use decorators (@asm_thumb, @asm_pio) that add names to the
function scope, that the linter cannot see.

It's useful to clear them in the file not in pyproject.toml as example code
will be copied and adapted elsewhere, and those developers may also use
Ruff (we hope!)

Signed-off-by: Angus Gratton <angus@redyak.com.au>

examples/rp2/pio_pinchange.py

@@ -8,6 +8,8 @@
 #   - setting an irq handler for a StateMachine
 #   - instantiating 2x StateMachine's with the same program and different pins
 
+# ruff: noqa: F821 - @asm_pio decorator adds names to function scope
+
 import time
 from machine import Pin
 import rp2