Run black against everything, not just tests and datasette dirs

tests/test_black.py

@@ -9,7 +9,5 @@ code_root = Path(__file__).parent.parent
 
 def test_black():
     runner = CliRunner()
-    result = runner.invoke(
-        black.main, [str(code_root / "tests"), str(code_root / "datasette"), "--check"]
-    )
+    result = runner.invoke(black.main, [str(code_root), "--check"])
     assert result.exit_code == 0, result.output