🧑‍💻 Add validate-pins workflow for PRs #5

	#
	# ci-validate-pins.yml
	# Validate that all of the pins files are unchanged by pinsformat.py
	#

	name: CI - Validate Pins Files

	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/**
	- test/**
	- Marlin/tests/**
	- '*/.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/**
	- test/**
	- Marlin/tests/**
	- '*/.md'

	jobs:
	validate_pins_files:
	name: Validate Pins Files
	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: Select Python 3.9
	uses: actions/setup-python@v5
	with:
	python-version: '3.9'
	architecture: 'x64'

	- name: Validate all pins files
	run: \|
	make validate-pins -j

Provide feedback