Wrap overflow: auto in media query for smaller screens only

[colorful-tones]

What?

Addresses #66161 and #66156

Why?

The appearance of double vertical scrollbars was occurring in certain instances of the interface where the viewport height was small. It seemed to be triggered by the overflow: auto, which had a previous code comment indicating that the overflow: auto was implemented to circumvent issues with mobile Safari. Based on the commentary it seems we would want the overflow: auto to only impact smaller horizontal screens and not smaller vertical screens.

How?

By wrapping the overflow: auto in a media query: @media (max-width: #{ ($break-medium - 1) }) we make sure the overflow is only applied to smaller horizontal screens.

Testing Instructions

The original bug reported in #66161 impacts small vertical screens.

1. Open the block editor on a desktop device with a small vertical height.
2. Open the block inserter sidebar and note the right-most vertical scrollbar(s)
3. Begin typing to find a block and note the right-most vertical scrollbar(s)

Screenshots or screencast

Before	After
double-scrollbar-before.mp4	double-scrollbar-after.mp4

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[colorful-tones]

Probably could use some more cross-device and browser size testing.

[colorful-tones]

This also addresses #66156

[dhruvang21]

Hello @colorful-tones,

I have tested this PR using the Gutenberg PR reviewer, as well as in my local Chrome and Firefox browsers across various screen sizes, and found that it resolves the issue perfectly. I’m also attaching a video of the testing for your reference.

Thanks!

66176-chrome.mp4