Tests: Add unit tests for wp_refresh_post_nonces()

[pbearne]

This ticket adds comprehensive unit tests for the wp_refresh_post_nonces() function in wp-admin/includes/misc.php. These tests ensure that the function correctly returns refreshed nonces for post locking and unlocking when appropriate Heartbeat data is provided and the user has the necessary permissions.

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Description:
This PR adds unit tests for the wp_refresh_post_nonces() function in wp-admin/includes/misc.php. These tests ensure that the function correctly refreshes post-related nonces (like getpermalinknonce, _wpnonce, etc.) during Heartbeat requests, while verifying user permissions and handling invalid post IDs.

The tests cover:

• Handling of missing or empty Heartbeat data.
• Validation of the post_id parameter (zero, string, non-numeric).
• Verification that no nonces are refreshed if the current user cannot edit the post.
• Successful generation and verification of all 5 nonces (getpermalinknonce, samplepermalinknonce, closedpostboxesnonce, _ajax_linking_nonce, and _wpnonce) when authorized.

Trac ticket: https://core.trac.wordpress.org/ticket/65197

AI Disclosure:

• AI assistance: Yes
• Tool(s): Junie (JetBrains)
• Model(s): gemini-3-flash-preview
• Used for: Code analysis, test implementation, and workflow management.