Make subprocess calls raise an exception on non-zero exit codes

[Sanqui]

The Python function subprocess.call() does not raise an exception when the command returns a non-zero exit code, i.e. it fails. This function is used in four places, but the most critical one is subprocess.call(["/usr/bin/ditto", f, f_in_image]). If not enough space is allocated for the .dmg, this command will fail and output to stderr,

ditto: /Volumes/Volume 1/foo.bar: No space left on device

Because the return code of this call is not validated, dmgbuild continues merrily, which can cause a broken release when happening as a part of a deployment process.

Replace all subprocess.call() functions with subprocess.check_call() to ensure that an error like this raises an exception and causes the process to fail. subprocess.check_call() is already used in other places in the code.

[Sanqui]

The tests fail, so I checked what gets printed to stderr:

E           subprocess.CalledProcessError: Command '['/usr/bin/ditto', '/System/Applications/TextEdit.app', '/Volumes/Test/TextEdit.app']' returned non-zero exit status 1.

/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/subprocess.py:369: CalledProcessError
------------------------------------------------------ Captured stderr call -------------------------------------------------------
ditto: /Volumes/Test/TextEdit.app/Contents: Operation not permitted

I believe the test was flawed to begin with and my change revealed this issue, but please let me know if I'm wrong -- I don't know much about Mac packaging. In any case, I'm not sure how I would fix the tests.