Unnecessary cast warnings when compiling tests with option -Wuseless-cast

[siddux]

I've found some warnings when compiling my tests using the -Wuseless-cast flag. The proposed changes seems to fix it.

--- stderr: robot_health_checker                                                                                                                                              
In file included from /opt/ros/humble/src/gtest_vendor/./src/gtest.cc:122,
                 from /opt/ros/humble/src/gtest_vendor/src/gtest-all.cc:41:
/opt/ros/humble/src/gtest_vendor/./src/gtest-internal-inl.h: In member function ‘virtual void testing::internal::StreamingListener::SocketWriter::Send(const string&)’:
/opt/ros/humble/src/gtest_vendor/./src/gtest-internal-inl.h:1091:24: warning: useless cast to type ‘size_t’ {aka ‘long unsigned int’} [-Wuseless-cast]
 1091 |       const auto len = static_cast<size_t>(message.length());
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /opt/ros/humble/src/gtest_vendor/src/gtest-all.cc:41:
/opt/ros/humble/src/gtest_vendor/./src/gtest.cc: In member function ‘std::string testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop(int)’:
/opt/ros/humble/src/gtest_vendor/./src/gtest.cc:821:7: warning: useless cast to type ‘int’ [-Wuseless-cast]
  821 |       static_cast<int>(GTEST_FLAG(stack_trace_depth)),
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/ros/humble/src/gtest_vendor/./src/gtest.cc: In static member function ‘static void testing::internal::XmlUnitTestResultPrinter::OutputXmlCDataSection(std::ostream*, const char*)’:
/opt/ros/humble/src/gtest_vendor/./src/gtest.cc:3754:20: warning: useless cast to type ‘std::streamsize’ {aka ‘long int’} [-Wuseless-cast]
 3754 |           segment, static_cast<std::streamsize>(next_segment - segment));
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
---

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