In `WP_Upgrader::delete_temp_backup()`, a malformed `sprintf()` call did not pass the value, triggering a Warning in PHP 7 and a Fatal Error in PHP 8.
This fixes the malformed `sprintf()` call by correctly passing the value.
Follow-up to [55720].
Props akihiroharai, afragen.
Merges [56550] to the 6.3 branch.
Fixes#59320.
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