docs: Add example and tests for `pl.concat()` with `Expr` #13794

	name: Lint Python

	on:
	pull_request:
	paths:
	- py-polars/**
	- .github/workflows/lint-python.yml

	concurrency:
	group: ${{ github.workflow }}-${{ github.ref }}
	cancel-in-progress: true

	jobs:
	ruff:
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4

	- name: Get ruff version from requirements file
	id: version
	run: \|
	VERSION=$(grep -m 1 -oP 'ruff==\K(.*)' py-polars/requirements-lint.txt)
	echo "version=$VERSION" >> $GITHUB_OUTPUT

	- uses: chartboost/ruff-action@v1
	with:
	src: py-polars/
	version: ${{ steps.version.outputs.version }}
	args: check --no-fix

	- uses: chartboost/ruff-action@v1
	with:
	src: py-polars/
	version: ${{ steps.version.outputs.version }}
	args: format --diff

	mypy:
	runs-on: ubuntu-latest
	strategy:
	fail-fast: false
	matrix:
	python-version: ['3.9', '3.12']

	steps:
	- uses: actions/checkout@v4

	- name: Set up Python
	uses: actions/setup-python@v5
	with:
	python-version: ${{ matrix.python-version }}

	- name: Create virtual environment
	run: \|
	curl -LsSf https://astral.sh/uv/install.sh \| sh
	uv venv
	echo "$GITHUB_WORKSPACE/.venv/bin" >> $GITHUB_PATH
	echo "VIRTUAL_ENV=$GITHUB_WORKSPACE/.venv" >> $GITHUB_ENV

	- name: Install Python dependencies
	working-directory: py-polars
	run: uv pip install -r requirements-dev.txt -r requirements-lint.txt

	# Allow untyped calls for older Python versions
	- name: Run mypy
	working-directory: py-polars
	run: mypy ${{ (matrix.python-version == '3.9') && '--allow-untyped-calls' \|\| '' }}

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