I have a really simple repo in GitHub (/Hooks/), currently containing just 1 file, a simple Hooks.ts typescript file. On my local machine, in my Workspace, I've created a project folder and I can yarn add normal repositories like yarn add fuse.js but I wanted to yarn add my private repo yarn add Hooks using this format yarn add git+ssh//git@github.com:OrganisationName/Hooks.git but I just get Error: couldn't find the binary git'. I have permissions to the Hooks repo because I can push/pull from it. I'm on OSX Mojave (10.14.16) and installed Yarn via brew. My yarn version (yarn -v) is 1.22.10. This is the latest brew will install after running brew upgrade yarn.
This error "couldn't find the binary git" is related with not having installed git where the installation is made, Are you running these. commands inside a container? you might as well be installing openssh, is necessary too.
for example in an alpine container
apk add --no-cache git openssh
yarn install
If, just in case, you don't want to access to the repo trough SSH, you can access trough https+deploy-token, heres a gitlab example:
git+https://<token-name>:<token>@gitlab.com/Username/Repository#<branch|tag>