月日を年月日に変換

dt_now = pd.Timestamp.now(tz="Asia/Tokyo").tz_localize(None)
df = pd.read_csv(url, parse_dates=True, index_col=0, date_parser=lambda x: datetime.datetime.strptime(x, "%m/%d").replace(year=dt_now.year))
df = pd.read_csv(url, parse_dates=True, index_col=0, date_parser=lambda x: pd.to_datetime(x, format="%m/%d").replace(year=dt_now.year))

今週の月曜日を取得

pd.to_datetime("today") + pd.offsets.Week(weekday=0) - pd.offsets.Week()

来週の月曜日を取得して、一週間戻す