Fix sidebar icon toggle logic for desktop and mobile views

[phsete]

Why:

The collapse and expand icons on the sidebar are swapped.
Closes: #45210

What's being changed (if available, include any code snippets, screenshots, or gifs):

The collapse and expand icons for the sidbar are swapped.

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• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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[Copilot]

Pull request overview

Corrects swapped sidebar icons across desktop and mobile layouts.

Changes:

• Reverses icon selection for collapsed desktop and open mobile states.
• Keeps labels and expanded-state semantics unchanged.

[heardjalissa9-gif]

Understood.

[heardjalissa9-gif]

Let's do it.