Fix Category List Block: Add optional chaining to taxonomy name

[Mayank-Tripathi32]

Fixes #69697

What?

This PR adds optional chaining (?.) for the name and labels.singular_name properties in the taxonomy object to prevent potential undefined errors.

Why?

Without optional chaining, the block may throw an error when the taxonomy data is unavailable or not properly set. This issue is noticeable when using the Category List block inside a pattern, particularly when enabling "Show as dropdown" and "Show empty values" options.

How?

The implementation adds optional chaining in relevant areas where the taxonomy object or its properties are accessed:

• Placeholder text for the dropdown (placeholder={ taxonomy?.name })
• The VisuallyHidden label (label ? label : taxonomy?.name)
• Dropdown option text (sprintf( __( 'Select %s' ), taxonomy?.labels?.singular_name ))

These changes ensure that the block does not break when the taxonomy object is missing or incomplete.

Testing Instructions

• Add a new pattern.
• Insert a Category List block into the pattern.
• Edit the label and enable Show as dropdown + Show empty values from the inspector panel.
• Add this pattern to the Site Editor and save the changes.
• Reload the editor and observe the Category List block.
• Previously, the block would sometimes show an error when the taxonomy data was unavailable. Now, it should function correctly without breaking.

ScreenCast

If it does not load then it would show (undefined) - Rarely

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Co-authored-by: Mayank-Tripathi32 <mayanktripathi32@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>
Co-authored-by: hagege <hage@git.wordpress.org>

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[Mamaduka]

Thank you, @Mayank-Tripathi32!