[dagster-dbt] Refactor UnitTestDefinition instantiation in utils.py to use from_dict method

Verified `test_dbt_with_unit_tests()` passes with both "fqn:*" and "tag:test" selectors.

Updated the instantiation of UnitTestDefinition in the __getattr__
method to utilize the from_dict method instead of the constructor. This
change enhances the clarity and consistency of the code when handling
unit test nodes from the manifest JSON.

Fixed: dagster-io#27007

Author: kang8

python_modules/libraries/dagster-dbt/dagster_dbt/utils.py

@@ -51,7 +51,7 @@ def __getattr__(self, item):
             {
                 "unit_tests": {
                     # unit test nodes must be of type UnitTestDefinition
-                    unique_id: UnitTestDefinition(**info)
+                    unique_id: UnitTestDefinition.from_dict(info)
                     for unique_id, info in manifest_json["unit_tests"].items()
                 },
             }