Doesn't work unless you provide a `--pk` about yaml-to-sqlite

[simonw]

The test already fails:

tmpdir = local('/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-210/test_without_pk0')

    def test_without_pk(tmpdir):
        db_path = tmpdir / "db.db"
>       assert (
            0
            == CliRunner()
            .invoke(cli.cli, [str(db_path), "items", "-"], input=TEST_YAML)
            .exit_code
        )
E       AssertionError: assert 0 == 1
E        +  where 1 = <Result PrimaryKeyRequired('upsert() requires a pk')>.exit_code
E        +    where <Result PrimaryKeyRequired('upsert() requires a pk')> = <bound method CliRunner.invoke of <click.testing.CliRunner object at 0x10a08a518>>(<Command cli>, ['/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-210/test_without_pk0/db.db', 'items', '-'], input='\n- name: datasette-cluster-map\n  url: https://github.com/simonw/datasette-cluster-map\n- name: datasette-vega\n  url: https://github.com/simonw/datasette-vega\n  nested_with_date:\n  - title: Hello\n    date: 2010-01-01\n')
E        +      where <bound method CliRunner.invoke of <click.testing.CliRunner object at 0x10a08a518>> = <click.testing.CliRunner object at 0x10a08a518>.invoke
E        +        where <click.testing.CliRunner object at 0x10a08a518> = CliRunner()
E        +      and   <Command cli> = cli.cli

tests/test_cli.py:32: AssertionError