Remove the fileapi.h include in os-inl.h (#3444)

* Replaced fileapi.h include with windows.h, as instructed in https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-flushfilebuffers
Otherwise this causes compilation error on older sdks.

* Removed the fileapi.h include entirely, since windows.h is already included before

---------

Co-authored-by: MasonAngelio <MasonAngelio>

include/spdlog/details/os-inl.h

@@ -23,7 +23,6 @@
 
 #ifdef _WIN32
     #include <spdlog/details/windows_include.h>
-    #include <fileapi.h>  // for FlushFileBuffers
     #include <io.h>       // for _get_osfhandle, _isatty, _fileno
     #include <process.h>  // for _get_pid
 

tests/CMakeLists.txt

@@ -75,7 +75,7 @@ function(spdlog_prepare_test test_target spdlog_lib)
     elseif(SPDLOG_SANITIZE_THREAD)
         spdlog_enable_thread_sanitizer(${test_target})
     endif()
-    add_test(NAME ${test_target} COMMAND ${test_target})
+    add_test(NAME ${test_target} COMMAND ${test_target} --order decl)
     set_tests_properties(${test_target} PROPERTIES RUN_SERIAL ON)
 endfunction()