chore(itam): add missing pytest mark serializer

ref:

pyproject.toml

@@ -1116,6 +1116,7 @@ markers = [
     "module_setings: Selects all tests from module settings.",
     "note_models: Selects all centurion model note models",
     "permissions: selects all permission related tests.",
+    "serializer: Selects all serializer tests",
     "tenancy_models: Selects Tenancy models.",
     "unit: Selects all Unit Tests.",
 ]