fix(FileInfo): correctly implement `\ArrayAccess::offsetGet`

We are targetting PHP 8.1+, since PHP 8.0 `offsetGet` has the `mixed` types for `offset` and return value.
So this adds the types to correctly implement the interface.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

lib/private/Files/FileInfo.php

@@ -95,11 +95,7 @@ class FileInfo implements \OCP\Files\FileInfo, \ArrayAccess {
 		unset($this->data[$offset]);
 	}
 
-	/**
-	 * @return mixed
-	 */
-	#[\ReturnTypeWillChange]
-	public function offsetGet($offset) {
+	public function offsetGet(mixed $offset): mixed {
 		return match ($offset) {
 			'type' => $this->getType(),
 			'etag' => $this->getEtag(),
@@ -164,7 +160,7 @@ class FileInfo implements \OCP\Files\FileInfo, \ArrayAccess {
 	 * @return string
 	 */
 	public function getEtag() {
-		$this->updateEntryfromSubMounts();
+		$this->updateEntryFromSubMounts();
 		if (count($this->childEtags) > 0) {
 			$combinedEtag = $this->data['etag'] . '::' . implode('::', $this->childEtags);
 			return md5($combinedEtag);
@@ -179,7 +175,7 @@ class FileInfo implements \OCP\Files\FileInfo, \ArrayAccess {
 	 */
 	public function getSize($includeMounts = true) {
 		if ($includeMounts) {
-			$this->updateEntryfromSubMounts();
+			$this->updateEntryFromSubMounts();
 
 			if ($this->isEncrypted() && isset($this->data['unencrypted_size']) && $this->data['unencrypted_size'] > 0) {
 				return $this->data['unencrypted_size'];
@@ -195,7 +191,7 @@ class FileInfo implements \OCP\Files\FileInfo, \ArrayAccess {
 	 * @return int
 	 */
 	public function getMTime() {
-		$this->updateEntryfromSubMounts();
+		$this->updateEntryFromSubMounts();
 		return (int)$this->data['mtime'];
 	}
 
@@ -318,7 +314,7 @@ class FileInfo implements \OCP\Files\FileInfo, \ArrayAccess {
 		$this->subMounts = $mounts;
 	}
 
-	private function updateEntryfromSubMounts(): void {
+	private function updateEntryFromSubMounts(): void {
 		if ($this->subMountsUsed) {
 			return;
 		}