fix s2s test - disable multitasking by setting multitask_config_yaml to None (#3059)

Summary:
# Before submitting

- [ ] Was this discussed/approved via a Github issue? (no need for typos, doc improvements)
- [ ] Did you read the [contributor guideline](https://github.com/pytorch/fairseq/blob/main/CONTRIBUTING.md)?
- [ ] Did you make sure to update the docs?
- [ ] Did you write any new necessary tests?

## What does this PR do?
Fixes # (issue).

## PR review
Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

## Did you have fun?
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Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/3059

Reviewed By: kahne

Differential Revision: D34083178

Pulled By: sravyapopuri388

fbshipit-source-id: a33af1696570be4826973b19fe34177bcf851e06

tests/speech/test_s2s_transformer.py

@@ -19,7 +19,8 @@ class TestS2STransformer(TestFairseqSpeech):
                 "dev_shuf200.tsv",
                 "src_feat.zip",
                 "config_specaug_lb.yaml",
-                "config_letter_enc_unigram_dec.yaml",
+                "vocoder",
+                "vocoder_config.json",
             ],
         )
 
@@ -30,10 +31,13 @@ class TestS2STransformer(TestFairseqSpeech):
             dataset="dev_shuf200",
             arg_overrides={
                 "config_yaml": "config_specaug_lb.yaml",
+                "multitask_config_yaml": None,
                 "target_is_code": True,
                 "target_code_size": 100,
+                "eval_inference": False,
             },
             score_type="bleu",
+            strict=False,
         )
 
     def postprocess_tokens(self, task, target, hypo_tokens):