[FIX] event_sale: fix unit test

Steps to reproduce:

- Install any localization account module
- Install event_sale
- Run the unit test :TestEventSale.test_ticket_price_with_currency_conversion

Current behaviour:
The unit test will fail in line 341

Expected behaviour:
The unit test should not fail

Explanation:
The unit test used self.env.company which will populate demo invoices after installing
the localization account module. Therefore we can't change the currency on the company
any more in event_sale/tests/test_event_sale.py line 341. It is better to create a new
company in the unit test to prevent side effect like this.

closes odoo/odoo#116777

X-original-commit: 105b48b5
Signed-off-by: William André (wan) <wan@odoo.com>