MQTT/Websocket: the username field must now match your account email

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What's changing

When connecting to the OpenF1 MQTT broker, the username field must be set to
your OpenF1 account email address. Previously any string was accepted.

Why

We use the username to track connections per account. When it doesn't match the
account, connections are attributed incorrectly, which can cause spurious
Not authorized (0x87) rejections. Requiring the real username removes that
class of failure.

What you need to do

If you already pass your account email, nothing changes. Otherwise, update your
client:

client.username_pw_set(
    username="your-account-email@example.com",  # must match your OpenF1 account
    password=ACCESS_TOKEN,
)

Connections with a mismatched username will be rejected with 0x87.