Support for RP2040 and BTT SKR Pico (WIP) #1680

	#
	# ci-unit-tests.yml
	# Build and execute unit tests to catch functional issues in code
	#

	name: CI - Unit Tests

	on:
	pull_request:
	branches:
	- bugfix-2.1.x
	# Cannot be enabled on 2.1.x until it contains the unit test framework
	#- 2.1.x
	paths-ignore:
	- config/**
	- data/**
	- docs/**
	- '*/.md'
	push:
	branches:
	- bugfix-2.1.x
	# Cannot be enabled on 2.1.x until it contains the unit test framework
	#- 2.1.x
	paths-ignore:
	- config/**
	- data/**
	- docs/**
	- '*/.md'

	jobs:
	# This runs all unit tests as a single job. While it should be possible to break this up into
	# multiple jobs, they currently run quickly and finish long before the compilation tests.
	run_unit_tests:
	name: Unit Test
	# These tests will only be able to run on the bugfix-2.1.x branch, until the next release
	# pulls them into additional branches.
	if: github.repository == 'MarlinFirmware/Marlin'

	runs-on: ubuntu-latest

	steps:
	- name: Check out the PR
	uses: actions/checkout@v4

	- name: Cache pip
	uses: actions/cache@v4
	with:
	path: ~/.cache/pip
	key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
	restore-keys: \|
	${{ runner.os }}-pip-

	- name: Cache PlatformIO
	uses: actions/cache@v4
	with:
	path: ~/.platformio
	key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}

	- name: Select Python 3.9
	uses: actions/setup-python@v5
	with:
	python-version: '3.9'
	architecture: 'x64'

	- name: Install PlatformIO
	run: \|
	pip install -U platformio
	pio upgrade --dev
	pio pkg update --global

	- name: Run All Unit Tests
	run: \|
	make unit-test-all-local

Provide feedback