fix: NotificationManager: Use the nick from a subscription request in notification and contact name

Fixes #10998.
10 jobs for subscription-request-nick-fix in 4 minutes and 8 seconds (queued for 99 minutes and 41 seconds)
Name Stage Failure
failed
test-pyright Test
/builds/bodqhrohro/gajim/gajim/gtk/notification_manager.py
/builds/bodqhrohro/gajim/gajim/gtk/notification_manager.py:337:69 - error: Argument of type "list[str | None]" cannot be assigned to parameter "strv" of type "list[str]" in function "new_strv"
  TypeVar "_T@list" is invariant
    Type "str | None" cannot be assigned to type "str"
      Type "None" cannot be assigned to type "str" (reportGeneralTypeIssues)
1 error, 0 warnings, 0 informations
Completed in 24.495sec
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
test-flake8 Test
Skipping Git submodules setup
Executing "step_script" stage of the job script
Using docker image sha256:34956a9c185f8fffc4ad062374f19553388ecc2a2bfae563a93536a5a510181a for gajim-master:latest ...
$ flake8
./gajim/gtk/notification_manager.py:337:81: E501 line too long (96 > 80 characters)
1 E501 line too long (96 > 80 characters)
1
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1