nixos/test-driver: fix OCR (#375091)

    tess_args = "-c debug_file=/dev/null --psm 11"

    cmd = f"convert {magick_args} '{screenshot_path}' 'tiff:{screenshot_path}.tiff'"

    cmd = f"magick convert {magick_args} '{screenshot_path}' '{screenshot_path}.png'"

    ret = subprocess.run(cmd, shell=True, capture_output=True)

    if ret.returncode != 0:

        raise Exception(f"TIFF conversion failed with exit code {ret.returncode}")

        raise Exception(

            f"Image processing failed with exit code {ret.returncode}, stdout: {ret.stdout.decode()}, stderr: {ret.stderr.decode()}"

        )

    model_results = []

    for model_id in model_ids:

        cmd = f"tesseract '{screenshot_path}.tiff' - {tess_args} --oem '{model_id}'"

        cmd = f"tesseract '{screenshot_path}.png' - {tess_args} --oem '{model_id}'"

        ret = subprocess.run(cmd, shell=True, capture_output=True)

        if ret.returncode != 0:

            raise Exception(f"OCR failed with exit code {ret.returncode}")