Needs update to newer googletest to build with gcc 15.1.0

[dschepler]

In a recent test of building from main, I get:

$ nice -n 19 cmake --build . -j1
[3/46] Building CXX object libshaderc_util/CMakeFiles/shaderc_util_counting_includer_test.dir/src/counting_includer_test.cc.o
FAILED: [code=1] libshaderc_util/CMakeFiles/shaderc_util_counting_includer_test.dir/src/counting_includer_test.cc.o 
/usr/bin/c++ -DENABLE_HLSL -I/tmp/shaderc/third_party/glslang -I/tmp/shaderc/libshaderc_util/include -isystem /tmp/shaderc/third_party/googletest/googlemock/include -isystem /tmp/shaderc/third_party/googletest/googletest/include -isystem /tmp/shaderc/third_party/googletest/googlemock -isystem /tmp/shaderc/third_party/googletest/googletest -Wimplicit-fallthrough -g -Wextra-semi -Wall -Werror -fvisibility=hidden -fPIC -Wno-noexcept-type -MD -MT libshaderc_util/CMakeFiles/shaderc_util_counting_includer_test.dir/src/counting_includer_test.cc.o -MF libshaderc_util/CMakeFiles/shaderc_util_counting_includer_test.dir/src/counting_includer_test.cc.o.d -o libshaderc_util/CMakeFiles/shaderc_util_counting_includer_test.dir/src/counting_includer_test.cc.o -c /tmp/shaderc/libshaderc_util/src/counting_includer_test.cc
In file included from /tmp/shaderc/third_party/googletest/googletest/include/gtest/internal/gtest-port.h:295,
                 from /tmp/shaderc/third_party/googletest/googlemock/include/gmock/internal/gmock-port.h:57,
                 from /tmp/shaderc/third_party/googletest/googlemock/include/gmock/internal/gmock-internal-utils.h:50,
                 from /tmp/shaderc/third_party/googletest/googlemock/include/gmock/gmock-actions.h:146,
                 from /tmp/shaderc/third_party/googletest/googlemock/include/gmock/gmock.h:56,
                 from /tmp/shaderc/libshaderc_util/src/counting_includer_test.cc:20:
/usr/include/c++/15.1.0/ciso646:46:4: error: #warning "<ciso646> is deprecated in C++17, use <version> to detect implementation-specific macros" [-Werror=cpp]
   46 | #  warning "<ciso646> is deprecated in C++17, use <version> to detect implementation-specific macros"
      |    ^~~~~~~
cc1plus: all warnings being treated as errors
ninja: build stopped: subcommand failed.