tests: notifications: increase indentation of multi-line for loop condition

Code in question is:

for foo in [
item1,
item2,
item3]:
action1
action2

With the above indentation, a quick glance at the code does not show where
the actions start.

Using a double indentation for line continuation avoids this problem:

for foo in [
item1,
item2,
item3]:
action1
action2

There are no actual code changes in this commit.