test_depsolve: Test with empty exclude-specs

The go json serialize process takes a nil slice and converts that to a
'null' instead of an '[]' or leaving off the field. This means that the
json generated by python is not representative of what is output by
images/dnfjson and we have not been properly testing
osbuild-depsolve-dnf5

Testing dnf5 depsolving *also* requires that libdnf5 be present in the
environment, which is a separate problem that still needs to be fixed.

tools/test/test_depsolve.py

@@ -42,7 +42,10 @@ def depsolve(pkgs, repos, root_dir, cache_dir, command):
             "root_dir": root_dir,
             "repos": repos,
             "transactions": [
-                {"package-specs": pkgs},
+                {
+                    "package-specs": pkgs,
+                    "exclude-specs": None
+                },
             ]
         }
     }