docs: Update to the Zoomable Packed Circle Example

[Giammaria]

• Trailing double quote in description - reported by @domoritz via comment in PR docs: Addition of an example: Zoomable Circle Packing #3841
• Additional adjustment to this example's width and height to match the regular circle packing example

[Giammaria]

Hey @domoritz, thank you for approving this. Pardon my ignorance, but is there any further action needed from me to satisfy the automated checks? I can't imagine that they're related to the minor changes that I made, but thought I'd ask. Thanks!