Fix `RealmModelIntegrationTest.test_inference_open_qa`
# What does this PR do?

The test `RealmModelIntegrationTest::test_inference_open_qa` fails since my PR #21000. This integration test creates a config manually by `config = RealmConfig()` and passes it to `from_pretrained`, therefore it doesn't have the attribute `searcher_seq_len` (which is removed in #21000).

Using `from_pretrained` without specifying `config` will load from the Hub checkpoint which has `searcher_seq_len` in the config (loaded via `super().__init__(..., **kwargs)`), and fix the test.


_The documentation is not available anymore as the PR was closed or merged._