[vcpkg baseline][opencensus-cpp] Set cxx standard to 14 for compatibility with abseil

[Thomas1664]

Describe the pull request

• What does your PR fix?

  Fixes build error because this port depends on abseil which requires C++ 14:

FAILED: _deps/abseil-build/absl/base/CMakeFiles/absl_base.dir/internal/unscaledcycleclock.cc.o 
/usr/bin/c++  -I/mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src -fPIC -g -Wall -Wextra -Wcast-qual -Wconversion-null -Wformat-security -Wmissing-declarations -Woverlength-strings -Wpointer-arith -Wundef -Wunused-local-typedefs -Wunused-result -Wvarargs -Wvla -Wwrite-strings -DNOMINMAX -std=gnu++11 -MD -MT _deps/abseil-build/absl/base/CMakeFiles/absl_base.dir/internal/unscaledcycleclock.cc.o -MF _deps/abseil-build/absl/base/CMakeFiles/absl_base.dir/internal/unscaledcycleclock.cc.o.d -o _deps/abseil-build/absl/base/CMakeFiles/absl_base.dir/internal/unscaledcycleclock.cc.o -c /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/internal/unscaledcycleclock.cc
In file included from /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/config.h:86,
                 from /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/attributes.h:37,
                 from /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/port.h:21,
                 from /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/internal/unscaledcycleclock.h:45,
                 from /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/internal/unscaledcycleclock.cc:15:
/mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/base/policy_checks.h:79:2: error: #error "C++ versions less than C++14 are not supported."
   79 | #error "C++ versions less than C++14 are not supported."
      |  ^~~~~
[2/187] /usr/bin/c++  -I/mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src -fPIC -g -Wall -Wextra -Wcast-qual -Wconversion-null -Wformat-security -Wmissing-declarations -Woverlength-strings -Wpointer-arith -Wundef -Wunused-local-typedefs -Wunused-result -Wvarargs -Wvla -Wwrite-strings -DNOMINMAX -std=gnu++11 -MD -MT _deps/abseil-build/absl/strings/CMakeFiles/absl_strings_internal.dir/internal/utf8.cc.o -MF _deps/abseil-build/absl/strings/CMakeFiles/absl_strings_internal.dir/internal/utf8.cc.o.d -o _deps/abseil-build/absl/strings/CMakeFiles/absl_strings_internal.dir/internal/utf8.cc.o -c /mnt/vcpkg-ci/buildtrees/opencensus-cpp/x64-linux-dbg/_deps/abseil-src/absl/strings/internal/utf8.cc

• Which triplets are supported/not supported? Have you updated the CI baseline?

  Remove Windows from CI baseline (covered by supports)

[github-actions]

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