Make occurrence notification tests more reliable

By cancelling/rejecting an occurrence that's on a later day, the tests
would now catch the email using the reservation date instead of the
occurrene date.

indico/modules/rb/notifications/notifications_test.py

@@ -122,7 +122,7 @@ def test_reservation_modification_emails_plaintext(snapshot, snapshot_name, crea
     'occurrence_rejection_email_to_manager.txt', 'occurrence_rejection_email_to_user.txt'
 ))
 def test_reservation_occurrence_emails_plaintext(snapshot, snapshot_name, create_reservation):
-    res = create_reservation(id=0, start_dt=datetime(2022, 11, 11, 13, 37), end_dt=datetime(2022, 11, 12, 14, 37))
+    res = create_reservation(id=0, start_dt=datetime(2022, 11, 10, 13, 37), end_dt=datetime(2022, 11, 12, 14, 37))
     occurrence = {'start_dt': datetime(2022, 11, 11, 13, 37), 'rejection_reason': 'A valid reason!'}
     _assert_snapshot(snapshot, snapshot_name, 'reservations', reservation=res, occurrence=occurrence)
 

indico/modules/rb/templates/emails/reservations/tests/occurrence_cancellation_email_to_user.txt

@@ -5,7 +5,7 @@ You have CANCELLED an occurrence of your booking on Friday 11/11/2022.
 Room: 1/2-3
 For: Guinea Pig
 Reason: Testing
-Dates: Friday 11/11/2022 - Saturday 12/11/2022
+Dates: Thursday 10/11/2022 - Saturday 12/11/2022
 Hours: 13:37 - 14:37
 
 Booking details:

indico/modules/rb/templates/emails/reservations/tests/occurrence_rejection_email_to_manager.txt

@@ -8,7 +8,7 @@ A valid reason!
 Room: 1/2-3
 For: Guinea Pig
 Reason: Testing
-Dates: Friday 11/11/2022 - Saturday 12/11/2022
+Dates: Thursday 10/11/2022 - Saturday 12/11/2022
 Hours: 13:37 - 14:37
 
 You can check the details of the booking here:

indico/modules/rb/templates/emails/reservations/tests/occurrence_rejection_email_to_user.txt

@@ -8,7 +8,7 @@ A valid reason!
 Room: 1/2-3
 For: Guinea Pig
 Reason: Testing
-Dates: Friday 11/11/2022 - Saturday 12/11/2022
+Dates: Thursday 10/11/2022 - Saturday 12/11/2022
 Hours: 13:37 - 14:37
 
 Booking details: