Use google `default` for auth when no `service_account_json` file specified #436

	name: Linting and Tests
	on:
	push:
	branches: ["main"]
	pull_request:

	jobs:
	check-code-style:
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4

	- name: Setup Poetry
	uses: matrix-org/setup-python-poetry@v1
	with:
	install-project: "false"
	python-version: "3.11"

	- run: poetry run tox -e check_codestyle

	check-types-mypy:
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4

	- name: Setup Poetry
	uses: matrix-org/setup-python-poetry@v1
	with:
	install-project: "false"
	python-version: "3.11"

	- run: poetry run tox -e check_types

	run-unit-tests:
	name: Unit tests
	needs: [check-code-style, check-types-mypy]
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v3
	- uses: actions/setup-python@v4
	with:
	python-version: "3.11"
	- run: python -m pip install -e .
	- run: python -m twisted.trial tests

	run-unit-tests-olddeps:
	name: Unit tests (old dependencies)
	needs: [ check-code-style, check-types-mypy ]
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v3
	- uses: actions/setup-python@v4
	with:
	python-version: "3.8"
	- name: Patch pyproject.toml to require oldest dependencies
	run: \|
	# Ugly. Could use something like https://pyproject-parser.readthedocs.io/en/latest/cli.html#info in the future.
	sed --in-place=.bak -e 's/>=/==/g' pyproject.toml
	diff pyproject.toml.bak pyproject.toml \|\| true # diff returns 1 if there is a change
	- name: Install Sygnal
	run: python -m pip install -e .
	- run: python -m twisted.trial tests

Provide feedback