Fix System test type in breeze (apache#43670)

* Fix System test type in breeze

Adjust the behaviour of the `System` test type in Breeze testing tests.
Remove the path appending to the beginning of the breeze command
(because as we've discussed before with the reorganization of our test
directories this creates a non-top level loading of a pytest plugin
which pytest disallows). This allow us to still specify the System test
type because that option controls other beahviours we need (like
disabling db init).

* Fix unit test

dev/breeze/src/airflow_breeze/utils/run_tests.py

@@ -170,7 +170,6 @@ def get_excluded_provider_args(python_version: str) -> list[str]:
     "Serialization": [
         "tests/serialization",
     ],
-    "System": ["tests/system"],
     "TaskSDK": ["task_sdk/tests"],
     "WWW": [
         "tests/www",
@@ -255,7 +254,7 @@ def convert_test_type_to_pytest_args(
         else:
             return [INTEGRATION_TESTS]
     if test_type == "System":
-        return [SYSTEM_TESTS]
+        return []
     if skip_provider_tests and test_type.startswith("Providers"):
         return []
     if test_type.startswith(PROVIDERS_LIST_EXCLUDE_PREFIX):

dev/breeze/tests/test_pytest_args_for_test_types.py

@@ -63,7 +63,7 @@
         ),
         (
             "System",
-            ["tests/system"],
+            [],
             False,
         ),
         (