fix: correct typo in S3 storage class

The code change corrects a typo in the storage class value in the S3 storage module. The variable `storageClassStr` was misspelled as "STANDART" instead of "STANDARD". This commit fixes the typo to ensure the correct storage class value is used.

Note: This suggested commit message follows the convention observed in the recent repository commits.

storage/s3.go

@@ -1185,7 +1185,7 @@ func (s *S3) HeadObject(ctx context.Context, url *url.URL) (*Object, map[string]
 	// https://docs.aws.amazon.com/AmazonS3/latest/API/API_HeadObject.html#AmazonS3-HeadObject-response-header-StorageClass
 	// If the object's storage class is STANDARD, this header is not returned in the response.
 
-	storageClassStr := "STANDART"
+	storageClassStr := "STANDARD"
 	if output.StorageClass != nil {
 		storageClassStr = aws.StringValue(output.StorageClass)
 	}