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/asmled.py

@@ -1,5 +1,9 @@
 # flash LED #1 using inline assembler
 # this version is overly verbose and uses word stores
+#
+# ruff: noqa: F821 - @asm_thumb decorator adds names to function scope
+
+
 @micropython.asm_thumb
 def flash_led(r0):
     movw(r1, (stm.GPIOA + stm.GPIO_BSRRL) & 0xFFFF)