Update sh -> bash in quantization.md

[mikekgfb]

Resolve one instance of #1436 where we say sh but mean bash (sh is not bash on every system).

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/torchchat/1437

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 460ef89 with merge base 83314c7 ():

NEW FAILURE - The following job has failed:

• Run the aoti runner with CUDA using stories / test-runner-aot-cuda / linux-job (gh)
  RuntimeError: Command docker exec -t 09dd066575ae3b5b76e4f89fa86bd7a925720f4b14f08fdcba1d1271b4b6605c /exec failed with exit code 1

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / runner-aoti (16-core-ubuntu) (gh) (trunk failure)
  Process completed with exit code 1.

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[Jack-Khuu]

Thanks for the fast fix