fix(storage): missing include

[dbolduc]

We probably lost a transient include from google/cloud/log.h in #13975

https://c3i.jfrog.io/c3i/misc/logs/pr/23695/4-linux-clang/google-cloud-cpp/2.23.0//e846e5adce243ac53f5c2319b7d1d0638f84c96a-build.txt

/home/conan/workspace/prod-v1/bsr/31134/fbecd/.conan/data/google-cloud-cpp/2.23.0/_/_/build/e846e5adce243ac53f5c2319b7d1d0638f84c96a/src/google/cloud/storage/internal/retry_object_read_source.cc:102:21: error: implicit instantiation of undefined template 'std::basic_stringstream<char>'
  std::stringstream os;
                    ^
/usr/local/bin/../include/c++/v1/iosfwd:142:32: note: template is declared here
    class _LIBCPP_TEMPLATE_VIS basic_stringstream;
                               ^
1 error generated.
make[2]: *** [google/cloud/storage/CMakeFiles/google_cloud_cpp_storage.dir/internal/retry_object_read_source.cc.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [google/cloud/storage/CMakeFiles/google_cloud_cpp_storage.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [all] Error 2

---

This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.76%. Comparing base (a0fc9dd) to head (0c7192e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14052      +/-   ##
==========================================
+ Coverage   93.21%   93.76%   +0.55%     
==========================================
  Files        2194     2281      +87     
  Lines      188251   198692   +10441     
==========================================
+ Hits       175474   186313   +10839     
+ Misses      12777    12379     -398     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.