Fix `TestJobFilesIntegration` initialization

`input_hda_dict` and `input_hda` are initialized once for all tests
in the class, i.e. they needed to be class attributes.

Fix the following error when running all tests in the class with
`./run_tests.sh -integration test/integration/test_job_files.py`:

```
self = <integration.test_job_files.TestJobFilesIntegration object at 0x73c52a002260>

    def test_read_fails_if_input_file_purged(self):
        job, _, _ = self.create_static_job_with_state("running")
        job_id, job_key = self._api_job_keys(job)
>       input_file_path = self.input_hda.get_file_name()
E       AttributeError: 'TestJobFilesIntegration' object has no attribute 'input_hda'
```

test/integration/test_job_files.py

@@ -18,6 +18,7 @@ API has gone too far.
 import io
 import os
 import tempfile
+from typing import Any
 
 import requests
 from sqlalchemy import select
@@ -40,6 +41,8 @@ TEST_TUS_CHUNK_SIZE = 1024
 class TestJobFilesIntegration(integration_util.IntegrationTestCase):
     initialized = False
     dataset_populator: DatasetPopulator
+    input_hda_dict: dict[str, Any]
+    input_hda: model.HistoryDatasetAssociation
 
     @classmethod
     def handle_galaxy_config_kwds(cls, config):
@@ -57,9 +60,11 @@ class TestJobFilesIntegration(integration_util.IntegrationTestCase):
             sa_session = self.sa_session
             stmt = select(model.HistoryDatasetAssociation)
             assert len(sa_session.scalars(stmt).all()) == 0
-            self.input_hda_dict = self.dataset_populator.new_dataset(history_id, content=TEST_INPUT_TEXT, wait=True)
+            TestJobFilesIntegration.input_hda_dict = self.dataset_populator.new_dataset(
+                history_id, content=TEST_INPUT_TEXT, wait=True
+            )
             assert len(sa_session.scalars(stmt).all()) == 1
-            self.input_hda = sa_session.scalars(stmt).all()[0]
+            TestJobFilesIntegration.input_hda = sa_session.scalars(stmt).all()[0]
             TestJobFilesIntegration.initialized = True
 
     def test_read_by_state(self):