Global network settings always report changes when test=True

Description of Issue

When a state containing network.system is applied in test mode, Salt always return changes to apply even if the current configuration is up-to-date.

Setup

system:
  network.system:
    - enabled: True
    - hostname: myhostname
    - apply_hostname: True

Steps to Reproduce Issue

Execute the state file bellow in test mode:

$ salt 'myhostname' state.highstate test=True

jid: 20200312054102028991
myhostname:
----------
          ID: system
    Function: network.system
      Result: None
     Comment: Global network settings are set to be updated:
              ---
              +++
              @@ -1,2 +1,11 @@
              -NETWORKING=yes

              -HOSTNAME=myhostname

              +# Configuration for networking init script being run during

              +# the boot sequence

              +

              +# Set to 'no' to skip interfaces configuration on boot

              +CONFIGURE_INTERFACES=yes

              +

              +# Don't configure these interfaces. Shell wildcards supported/

              +#EXCLUDE_INTERFACES=

              +

              +# Set to 'yes' to enable additional verbosity

              +#VERBOSE=no
     Started: 05:41:04.898364
    Duration: 2.225 ms
     Changes:

Summary for myhostname
-------------
Succeeded: 56 (unchanged=1)
Failed:     0
-------------
Total states run:     56
Total run time:  474.120 ms

Salt return changes to be made.

Then run the same state without test mode enabled:

$ salt 'myhostname' state.highstate

jid: 20200312055319027869
myhostname:

Summary for myhostname
-------------
Succeeded: 56
Failed:     0
-------------
Total states run:     56
Total run time:  808.170 ms

Versions Report

Salt Version:
           Salt: 2019.2.3

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.7.3
      docker-py: Not Installed
          gitdb: 2.0.5
      gitpython: 2.1.11
          ioflo: Not Installed
         Jinja2: 2.10
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.7.3 (default, Dec 20 2019, 18:57:59)
   python-gnupg: Not Installed
         PyYAML: 3.13
          PyZMQ: 17.1.2
           RAET: Not Installed
          smmap: 2.0.5
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.1

System Versions:
           dist: debian 10.3
         locale: UTF-8
        machine: x86_64
        release: 4.19.0-8-cloud-amd64
         system: Linux
        version: debian 10.3

Start by reproducing the network.system state with state.highstate test=True from the issue, then compare its result with the same state without test mode. The issue is done when an up-to-date configuration reports no changes in test mode while still identifying real changes.