Remove sys.exit call in inspect_objects() and add test

tests/test_inspect_pkg.py

@@ -11,8 +11,8 @@
 from conda.core.prefix_data import PrefixData
 
 from conda_build.exceptions import CondaBuildUserError
-from conda_build.inspect_pkg import inspect_linkages, which_package
-from conda_build.utils import on_win
+from conda_build.inspect_pkg import inspect_linkages, inspect_objects, which_package
+from conda_build.utils import on_mac, on_win
 
 
 def test_which_package(tmp_path: Path):
@@ -289,3 +289,9 @@ def test_inspect_linkages_on_win():
 def test_inspect_linkages_not_installed():
     with pytest.raises(CondaBuildUserError):
         inspect_linkages(["not_installed_pkg"])
+
+
+@pytest.mark.skipif(on_mac, reason="inspect_objects is only available on macOS")
+def test_inspect_objects_not_on_mac():
+    with pytest.raises(CondaBuildUserError):
+        inspect_objects([])