Resolve #3408835 "Sqlitedatabaseexcluder accidentally includes"

Closes #3408835

package_manager/src/PathExcluder/SqliteDatabaseExcluder.php

@@ -29,9 +29,7 @@ class SqliteDatabaseExcluder implements EventSubscriberInterface {
    */
   public function __construct(
     private readonly PathFactoryInterface $pathFactory,
-    // TRICKY: this cannot be private nor readonly for testing purposes.
-    // @see \Drupal\Tests\package_manager\Kernel\PathExcluder\SqliteDatabaseExcluderTest::mockDatabase()
-    protected Connection $database
+    private readonly Connection $database,
   ) {}
 
   /**