fix(authentication): switch authentication mode

[MatthiasMichel]

Description:

• function fails with {'message': 'Not authenticated'}
• move to different headers and authentication solves the problem

Steps to reproduce:

• Demo code, modify uid_to_update, username and password

import asyncio

from config import password, username
from spond import spond

async def main():
    s = spond.Spond(username=username, password=password)
    uid_to_update = "xxxxxxxxxxx"
    updates = {
        'heading': "print",
        'description': "New Description with changes",
        # Add other updates as needed
    }

    try:
        await s.update_event(uid_to_update, updates)
        print("Event updated successfully.")
    except Exception as e:
        print(f"Failed to update event: {e}")

    await s.clientsession.close()

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)
asyncio.run(main())

Expected behavier:

• authentication is successful

[Olen]

LGTM