test: network menu snaphots (#27311)

## **Description**

Adds additional snapshots unit tests for the network form. And fixes the
existing one. It was only snapshotting an empty `<div />`. Because of
how modals work, you have to snapshot `baseElement` instead of
`container`.


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## **Related issues**



## **Manual testing steps**



## **Screenshots/Recordings**

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### **Before**

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### **After**

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## **Pre-merge author checklist**

- [ ] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

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Co-authored-by: salimtb <[email protected]>
Co-authored-by: MetaMask Bot <[email protected]>
Co-authored-by: David Walsh <[email protected]>
Co-authored-by: Howard Braham <[email protected]>
Co-authored-by: Maarten Zuidhoorn <[email protected]>