With 2.83 using bpy.ops.wm.save_mainfile print a double message that the file has been saved, but it correctly is saved only once:
paulm@cmstorm 13:51:~$ strace -o out blender -b --python-expr 'import bpy; bpy.ops.wm.save_mainfile(filepath="/tmp/doh.blend")'
Blender 2.83.0 (hash 211b6c29f771 built 2020-06-03 21:46:59)
Read prefs: /home/paulm/.config/blender/2.83/config/userpref.blend
Info: Saved "doh.blend"
Info: Saved "doh.blend"
Blender quit
paulm@cmstorm 13:51:~$ grep doh.blend out
stat("/tmp/doh.blend", 0x7fff0c60c3d0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/tmp/doh.blend@", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 12
stat("/tmp/doh.blend", 0x7fff0c60b720) = -1 ENOENT (No such file or directory)
stat("/tmp/doh.blend@", {st_mode=S_IFREG|0644, st_size=659964, ...}) = 0
stat("/tmp/doh.blend", 0x7fff0c60b700) = -1 ENOENT (No such file or directory)
rename("/tmp/doh.blend@", "/tmp/doh.blend") = 0
stat("/tmp/doh.blend", {st_mode=S_IFREG|0644, st_size=659964, ...}) = 0
write(1, "Saved \"doh.blend\"", 17) = 17
write(1, "Info: Saved \"doh.blend\"\n", 24) = 24
Is this worthy to report as a bug? It’s pretty minor, but it might give the impression that the file was incorrectly saved twice. In 2.81 nothing was printed as far as I can tell (so maybe 2.83 is trying to compensate 
)