I’ve been able to reproduce the issue. 
The following steps work as expected, but they diverge quite a bit from what I recall from previous tests:
on: push
jobs:
run:
runs-on: ubuntu-latest
steps:
- uses: iterative/setup-dvc@v1
- run: |
git init
dvc init
dvc remote add origin gdrive://root
dvc remote modify origin --local gdrive_use_service_account true
dvc remote modify origin --local gdrive_service_account_json_file_path /dev/null
date > file
dvc add file
dvc push --remote origin
env:
GDRIVE_CREDENTIALS_DATA: ${{ secrets.ORIGINAL_SERVICE_ACCOUNT_JSON }}