Fix regression Minz_Configuration (#7765)

Follow-up of https://github.com/FreshRSS/FreshRSS/pull/7761
Partially avoid calls to deprecated functions.
Avoid warnings:
```
[warning] --- old_entries does not exist in configuration
[warning] --- keep_history_default does not exist in configuration
```

lib/Minz/Configuration.php

@@ -231,25 +231,25 @@ class Minz_Configuration {
 	 * @return array<int|string,mixed>|null
 	 */
 	public function attributeArray(string $key): ?array {
-		$a = self::param($key, null);
+		$a = $this->data[$key] ?? null;
 		return is_array($a) ? $a : null;
 	}
 
 	/** @param non-empty-string $key */
 	public function attributeBool(string $key): ?bool {
-		$a = self::param($key, null);
+		$a = $this->data[$key] ?? null;
 		return is_bool($a) ? $a : null;
 	}
 
 	/** @param non-empty-string $key */
 	public function attributeInt(string $key): ?int {
-		$a = self::param($key, null);
+		$a = $this->data[$key] ?? null;
 		return is_numeric($a) ? (int)$a : null;
 	}
 
 	/** @param non-empty-string $key */
 	public function attributeString(string $key): ?string {
-		$a = self::param($key, null);
+		$a = $this->data[$key] ?? null;
 		return is_string($a) ? $a : null;
 	}