Editor: Allow Publish meta box action row to wrap.

[abhishekfdd]

Convert #major-publishing-actions to flex-wrap so third-party buttons injected via post_submitbox_misc_actions or post_submitbox_start fall to a new line instead of crowding the Move to Trash / Publish row.

Regression from [61645], which switched the container from floats to flex with space-between. Verified with WP Rocket and Yoast Duplicate Post.

Fixes #65286.

Trac ticket: https://core.trac.wordpress.org/ticket/65286

Testing instructions

1. Install and activate WP Rocket (or Yoast Duplicate Post — free).
2. Edit any post.
3. Observe in the Publish meta box: "Move to Trash" is crowded between
   the plugin-injected button and Publish/Update.
4. Apply this patch.
5. Reload the editor — the injected button now wraps to its own line and
   "Move to Trash" / Publish are spaced cleanly. Default no-plugin layout
   is unchanged.

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Props abhishekfdd.

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[github-actions]

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