force `subprocess.run` to check return code is 0

In general, this should help to capture unintentional errors.

Where the change has created failures, they have been fixed. (Mostly because the git repository that was looked for was missing.)

tests.py

@@ -58,7 +58,7 @@ def test_prepare_environment(tmp_path):
 
     # now call the function we want to test
     result = mod.prepare_environment(
-        mpsd_release=mpsd_release_to_test, script_dir=(script_dir)
+        mpsd_release=mpsd_release_to_test, script_dir=script_dir
     )
     # wait for 20 seconds for the git clone to finish
     # time.sleep(20)