Cable _terminations_modified set even if not modified

[arthanson]

NetBox version

v3.4.1

Python version

3.8

Steps to Reproduce

1. put a breakpoint or print statement on a_terminations setter (https://github.com/netbox-community/netbox/blob/develop/netbox/dcim/models/cables.py#L121)
2. Edit a cable and save it (making no modifications)
3. See that the breakpoint is hit and therefore _terminations_modified is set.

This is a problem as the signal handler (https://github.com/netbox-community/netbox/blob/develop/netbox/dcim/signals.py#L84) will check _terminations_modified and create a new cablepath.

Expected Behavior

_terminations_modified should only get set if the terminations are actually changed.

Observed Behavior

_terminations_modified is set even if terminations are not changed.