gitian building works perfectly, but failing windows signed build

[gdiscord]

Followed the gitian building instructions here, and everything works absolutely fine except on the windows signing.
https://github.com/jonatack/bitcoin-development/blob/master/gitian-building.md

specifically when this command is executed:

bin/gbuild -i --commit signature=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-win-signer.yml

Output (last 10 lines):

• read i
  ++ basename /home/ubuntu/build/unsigned/unsigned/testgitian-1.0-win64-setup-unsigned.exe
• INFILE=testgitian-1.0-win64-setup-unsigned.exe
  ++ echo testgitian-1.0-win64-setup-unsigned.exe
  ++ sed s/-unsigned//
• OUTFILE=testgitian-1.0-win64-setup.exe
• ./osslsigncode attach-signature -in /home/ubuntu/build/unsigned/unsigned/dtestgitian-1.0-win64-setup-unsigned.exe -out /home/ubuntu/out/testgitian-1.0-win64-setup.exe -sigin /home/ubuntu/build/signature/win/testgitian-1.0-win64-setup-unsigned.exe.pem
  Failed to open file: /home/ubuntu/build/signature/win/testgitian-1.0-win64-setup-unsigned.exe.pem

=========

The error is rather ambiguous. My initial thoughts were that the file didn't exist, but after have tried making the referenced file available in several places within the build environment, by editing the relevant file gitian-win-signer.yml , but without success, I need another set of eyes to look at it and offer suggestions for resolving it.

Do I need to manually create the .pem file?

the macos section all worked fine for both unsigned and signed without me doing anything else apart from what the instruction says., So I'm a little puzzled that windows works for unsigned but fails for the signed.

Also, I notice there is no signing instructions for linux. Any reasons why?