Fix typo in sentence, add missing 'to' in 'we need account for'

[Andir16]

Changes

In the notebook "Introduction to Quantum Error Correction via the Repetition Code" in the chapter "Storing Qubits" there is a small typo where the "to" is missing the following sentence:

"In all cases, we need account for the fact that errors do not only occur when something happens (like a gate or measurement), they also occur when the qubits are idle."

This PR corrects the sentence to:
"In all cases, we need to account for the fact that errors do not only occur when something happens (like a gate or measurement), they also occur when the qubits are idle."

No issue exists for this error. I thought it would be easier to simply create the PR, but could, of course, still create an issue if needed/desired.

URL to Notebook: https://learn.qiskit.org/course/quantum-hardware/introduction-to-quantum-error-correction-via-the-repetition-code

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