Fix formatting string in benchmark pretty printer

# Rows:

#   Benchmark

@dataclasses.dataclass(frozen=True)

class Key():

    pass

class Column():

    def __init__(self):

        pass

def lunch_str(d):

    "Convert a lunch dict to a string"

    return f"{d['TARGET_PRODUCT']}-{d['TARGET_RELEASE']}-{d['TARGET_BUILD_VARIANT']}"

        for key, column in summary["columns"]:

            for id, cell in column:

                duration_ns = statistics.median([b["duration_ns"] for b in cell])

                table.Set(tuple([summary["date"].strftime("YYYY-MM-DD"),

                table.Set(tuple([summary["date"].strftime("%Y-%m-%d"),

                                 summary["branch"],

                                 summary["tag"]]

                                + list(key)),