openssl: fix format type in ECH code

[vvb2060]

curl-android/curl/src/main/native/curl/lib/vtls/openssl.c:3943:70: error: format specifies type 'long' but the argument has type 'size_t' (aka 'unsigned int') [-Werror,-Wformat]
  3943 |             infof(data, "ECH: imported ECHConfigList of length %ld", elen);
       |                                                                ~~~   ^~~~
       |                                                                %zu
curl-android/curl/src/main/native/curl/lib/curl_trc.h:76:27: note: expanded from macro 'infof'
    76 |          Curl_infof(data, __VA_ARGS__); } while(0)
       |                           ^~~~~~~~~~~
 1 error generated.

[bagder]

Thanks!