chore: better type hints for `getAvailability`

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/private/Files/Cache/Storage.php

@@ -126,7 +126,7 @@ class Storage {
 	}
 
 	/**
-	 * @return array [ available, last_checked ]
+	 * @return array{available: bool, last_checked: int}
 	 */
 	public function getAvailability() {
 		if ($row = self::getStorageById($this->storageId)) {

lib/private/Files/Storage/Common.php

@@ -711,7 +711,7 @@ abstract class Common implements Storage, ILockingStorage, IWriteStreamStorage,
 	}
 
 	/**
-	 * @return array [ available, last_checked ]
+	 * @return array{available: bool, last_checked: int}
 	 */
 	public function getAvailability(): array {
 		return $this->getStorageCache()->getAvailability();