Run package substitution tests outside the parallel suite

Tests that upload a different artifact under the shelf-reader tar.gz
filename leave incorrect global content that can break parallel PyPI JSON
checks. Legit shelf-reader uploads and syncs remain parallel.

Assisted-by: Cursor
Co-authored-by: Cursor <cursoragent@cursor.com>

Author: gerrod3

pulp_python/tests/functional/api/test_crud_content_unit.py

@@ -203,7 +203,6 @@ def test_package_creation_with_metadata(
     )
 
 
-@pytest.mark.parallel
 def test_disallow_package_substitution(
     monitor_task,
     python_bindings,
@@ -272,7 +271,6 @@ def test_disallow_package_substitution(
     assert repo.latest_version_href.endswith("/2/")
 
 
-@pytest.mark.parallel
 def test_package_substitution_allowed_by_default(
     monitor_task,
     python_bindings,