Liquibase uses the alter table syntax to drop unique constraints.

Laravel 7 Illuminate affected

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

Schema::table('settings', function (Blueprint $table) {
        $table->dropUnique('settings_name_unique');
        $table->string('group')->default('default');
});

More cross-refs: #65885 #65929

There was once upon a time, a half measure to allow this syntax for unique constraints which were not marked as "created explicitly" to be dropped in this way. It seems to have been removed at some point. My vote would be that we give up on this bookkeeping, or revive it, but either way, permit this syntax where it is reasonable.