Remove Group block inner container from Grid variation in classic themes

[tellthemachines]

Trac ticket: https://core.trac.wordpress.org/ticket/61635

Syncs WordPress/gutenberg#49387 to core.

Testing in TT1, a grid that looks like this in the editor:

Should now look like this in the front end:

Instead of looking like this:

The remaining discrepancy between editor and front end is due to a pseudo-element that TT1 inserts into all Group blocks. There's a fix for that open in #7001.

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[github-actions]

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Props isabel_brison, aaronrobertshaw, andrewserong.

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[aaronrobertshaw]

Thanks for the test instructions and screenshots @tellthemachines, made review nice and easy 🙇

✅ Code changes match Gutenberg PR
✅ Tests as expected
✅ Applying along side fix from #7001 results in parity between editor and frontend

Before	After	With TT1 Fix

Block markup used

<!-- wp:group {"layout":{"type":"grid","columnCount":"4","minimumColumnWidth":null}} -->
<div class="wp-block-group"><!-- wp:paragraph {"backgroundColor":"black"} -->
<p class="has-black-background-color has-background">Grid 1</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"backgroundColor":"gray"} -->
<p class="has-gray-background-color has-background">Grid 2</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"style":{"layout":{"columnSpan":2,"rowSpan":1}},"backgroundColor":"blue"} -->
<p class="has-blue-background-color has-background">Grid 3</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"style":{"layout":{"columnSpan":2,"rowSpan":1}},"backgroundColor":"red"} -->
<p class="has-red-background-color has-background">Grid 4</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"style":{"layout":{"columnSpan":2,"rowSpan":1}},"backgroundColor":"orange"} -->
<p class="has-orange-background-color has-background">Grid 5</p>
<!-- /wp:paragraph --></div>
<!-- /wp:group -->

[github-actions]

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[andrewserong]

This is testing nicely for me, too!

[tellthemachines]

Thanks for the reviews! Committed to trunk in r58708.