Replace Travis with GitHub actions and fix many typos (#1657)

* Create django.yml

* Fix working directory

* ..

* .

* ..

* a.

* ..

* .

* Fix typo

* Install hunspell

* maxfail

* Fix install

* .

* Reduce number of typos

* Even less typos

* Postgres debug

* Spelling fixes, yet again

* Postgres with PW

* Fix failing test

* New workflows

* Fix syntax error

* Install gettext

* Test aginst python 3.6 as well

* Clean up strategies

* Add badge, do not ignore migrations

* Use pip cache

src/pretix/base/services/cart.py

@@ -1108,7 +1108,7 @@ def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, lo
     :param event: The event ID in question
     :param items: A list of dicts with the keys item, variation, count, custom_price, voucher, seat ID
     :param cart_id: Session ID of a guest
-    :raises CartError: On any error that occured
+    :raises CartError: On any error that occurred
     """
     with language(locale):
         ia = False