Call ports_changed on the multi-kernel-manager instead of the kernel manager

[Zsailer]

Fixes #1086.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.92%. Comparing base (08697b0) to head (88c8db5).
Report is 280 commits behind head on main.

Files	Patch %	Lines
...ter_server/services/kernels/connection/channels.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1088      +/-   ##
==========================================
- Coverage   77.98%   77.92%   -0.07%     
==========================================
  Files          68       68              
  Lines        8299     8299              
  Branches     1649     1649              
==========================================
- Hits         6472     6467       -5     
- Misses       1426     1430       +4     
- Partials      401      402       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[blink1073]

Thanks!