fix release build (constness via telemetry, not seen in debug)

Author: karlseguin

src/http/Http.zig

@@ -195,7 +195,7 @@ pub const Connection = struct {
     pub fn request(self: *const Connection) !u16 {
         const easy = self.easy;
 
-        const header_list = try Headers.init();
+        var header_list = try Headers.init();
         defer header_list.deinit();
         try self.secretHeaders(&header_list);
         try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_HTTPHEADER, header_list.headers));