[Doc] Add Mistral-7b-v0.3 model to the batch invariance validated model (#34584)

Signed-off-by: Parth Bansal <parthbansal127@gmail.com>

docs/features/batch_invariance.md

@@ -109,6 +109,7 @@ Batch invariance has been tested and verified on the following models:
 - **Qwen2.5**: `Qwen/Qwen2.5-0.5B-Instruct`, `Qwen/Qwen2.5-1.5B-Instruct`, `Qwen/Qwen2.5-3B-Instruct`, `Qwen/Qwen2.5-7B-Instruct`, `Qwen/Qwen2.5-14B-Instruct`, `Qwen/Qwen2.5-32B-Instruct`
 - **Llama 3**: `meta-llama/Llama-3.1-8B-Instruct`, `meta-llama/Llama-3.2-1B-Instruct`
 - **GPT-OSS**: `openai/gpt-oss-20b`, `openai/gpt-oss-120b`
+- **Mistral**: `mistralai/Mistral-7B-v0.3`
 
 Other models may also work, but these have been explicitly validated. If you encounter issues with a specific model, please report them on the [GitHub issue tracker](https://github.com/vllm-project/vllm/issues/new/choose).