tests: internal: signv4: fixed leak

Signed-off-by: Leonardo Alminana <leonardo.alminana@chronosphere.io>

Author: Leonardo Alminana

tests/internal/signv4.c

@@ -187,6 +187,8 @@ static struct request *http_request_create(char *request)
         start = sep + 1;
         br = strchr(start, '\n');
         if (!br) {
+            flb_sds_destroy(key);
+
             break;
         }