Mobile layout breaks on post list table during plugin update

[joedolson]

When a plugin update is triggered, the layout shifts and the left border is doubled.

On narrow viewports the plugin update row does not fill the width of the list table row, and the active plugin's left border is drawn twice.

Responsive list table rows became flex containers in [62958], but the update row kept the pre-flex :before pseudo-cell that mimicked the checkbox column. As a flex item it paints a second left border beside the row's own and leaves the update cell sized to its content. This removes the obsolete pseudo-cell and gives the cell a full-width flex basis.

Scoped to the max-width: 782px block, so desktop rendering is unchanged.

Trac ticket: https://core.trac.wordpress.org/ticket/65956

## Use of AI Tools

Trac ticket:

## Use of AI Tools

Closing in favor of ​https://github.com/WordPress/wordpress-develop/pull/13259

[arkaprabhachowdhury]

WP Playground mobile test evidence for PR #13259

[arkaprabhachowdhury]

Tested PR #13259 in WordPress Playground.

Environment: WordPress 7.2-alpha-20260825.043926, PHP 7.4.33, Chrome, 480x800 viewport. Installed Akismet 5.3.1 to create a reproducible update notice.

Results:

• PASS: At 480px, the plugin update notice renders as one full-width row without the duplicated left border. The row measured 441px wide; its only cell measured 441px, flex-basis was 100%, and the cell had no left border.
• PASS: At 1920px, the notice remains a normal table-row and spans 1716px, confirming desktop rendering is unchanged.

Screenshot: attached (Playground mobile evidence).

[joedolson]

In 63452:

Administration: Fix plugin update row in narrow viewports.

Update CSS for active plugin updates to account for the changes in list table structure in r62958, which did not account for how plugin updates display notices in mobile viewports. Remove doubled left border and stabilize layout.

Props khokansardar, sukhendu2002, arkaprabhachowdhury, joedolson.
Fixes #65956.

[joedolson]

Reopening for merge to 7.1.1.

[adamsilverstein]

Nice one @joedolson! Would you like to handle the backport here as well, or can I handle that for you?

[adamsilverstein]

+1 approved for 7.1.1 backport

[joedolson]

In 63484:

Administration: Fix plugin update row in narrow viewports.

Update CSS for active plugin updates to account for the changes in list table structure in r62958, which did not account for how plugin updates display notices in mobile viewports. Remove doubled left border and stabilize layout.

Reviewed by adam silverstein.
Merges [63452] to the 7.1 branch.

Props khokansardar, sukhendu2002, arkaprabhachowdhury, joedolson.
Fixes #65956.