Media Library: Fix filter toolbar loading spinner alignment

[yogeshbhutkar]

Trac ticket: https://core.trac.wordpress.org/ticket/65275

What?

Fixes the Media Library loading spinner alignment in the secondary filter toolbar.

Why?

With the toolbar using a grid layout for filter controls, the spinner could fall out of place depending on which filters were rendered. That also caused an unintended scrollbar in the filter area because the spinner no longer appeared adjacent to the filters.

How?

Keeps the existing grid layout intact and positions the spinner relative to .media-toolbar-secondary, so it stays aligned at the end of the toolbar and loads adjacent to the filters.

Screenshots

Before	After

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5.4
Used for: Initial code skeleton; final implementation was reviewed and edited by me.

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[github-actions]

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[github-actions]

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Props yogeshbhutkar, dhruvang21.

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[dhruvang21]

@yogeshbhutkar Tested using the WP playground seems to work fine in desktop view but we need to fix it in responsive views