GitHub Pages error on Windows

I am using GitHub Pages to store the outputs files from CI builds, with each build being stored to its own branch. This works on Linux and Mac, but is failing on Windows with the following error:

cd C:/Users/travis/AppData/Local/Temp/d20191011-1008-wgtfth/work
The source and destination cannot both be remote.
rsync error: syntax or usage error (code 1) at main.c(1274) [Receiver=3.1.2]
Could not copy C:/Users/travis/build/johnwason/robotraconteur/build/out.