fix grader workflow by using '$GITHUB_ENV' for setting environment variables instead of the deprecated 'set-env'
fix grader workflow by using '$GITHUB_ENV' for setting environment
variables instead of the deprecated 'set-env'

cksystemsteaching/selfie,cksystemsteaching/selfie,ChristianMoesl/selfie,cksystemsteaching/selfie,ChristianMoesl/selfie