Fix: Ensure block transformation works in the example

[aberllin]

Description
I noticed that the current example for toggling a code block using the backtick key doesn't work as expected. The issue occurs because Editor.nodes() can return text nodes instead of block elements, causingTransforms.setNodes() to fail.

To fix this, I added an extra check using Element.isElement(n), ensuring that only block elements are transformed.

Issue
Slate docs - Applying Custom Formatting

Example
Before the fix:
Pressing the backtick key sometimes fails to toggle a code block due to Transforms.setNodes() being applied to text nodes - demo.

After the fix:
The backtick key now correctly toggles a code block, as the logic ensures only block elements are transformed - demo

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

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Latest commit: b0f3ea5

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