Fix macOS build in github actions

[akshaynexus]

macOS Builds on github actions fails with unable to find unistd.h file.Needs looking into

[akshaynexus]

Here is a small snippet of the error

In file included from libs/thread/src/pthread/thread.cpp:9:
In file included from ./boost/thread/detail/config.hpp:11:
In file included from ./boost/config.hpp:57:
In file included from ./boost/config/platform/macos.hpp:28:
./boost/config/posix_features.hpp:18:15: fatal error: 'unistd.h' file not found
#     include <unistd.h>
              ^~~~~~~~~~````