HuggingFacePipeline._generate rejects valid translation tasks due to substring check

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [x] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs #40094 ### Reproduction Steps / Example Code (Python) ```python from unittest.mock import MagicMock from langchain_huggingface import HuggingFacePipeline # A real transformers translation pipeline reports its task as # "translation_xx_to_yy" (e.g. "translation_en_to_fr"), not "translation". pipe = MagicMock() pipe.task = "translation_en_to_fr" pipe.model.name_or_path = "mock-model-id" pipe.return_value = [{"translation_text": "Bonjour le monde"}] llm = HuggingFacePipeline(pipeline=pipe) result = llm._generate(["Hello world"]) print(result.generations[0][0].text) ``` ### Error Message and Stack Trace (if applicable) ```shell ValueError: Got invalid task translation_en_to_fr, currently only ('text2text-generation', 'text-generation', 'image-text-to-text', 'summarization', 'translation') are supported ``` ### Description * I'…