adding tuf root env variable

[cpanato]

Summary

Getting this error while doing the release

Step #3:   ⨯ release failed after 4m47s                       error=sign: cosign failed: exit status 1: Using payload from: /workspace/go/src/sigstore/fulcio/dist/fulcio-linux-ppc64le
Step #3: Generating ephemeral keys...
Step #3: Retrieving signed certificate...
Step #3: 
Step #3:         Note that there may be personally identifiable information associated with this signed artifact.
Step #3:         This may include the email address associated with the account with which you authenticate.
Step #3:         This information will be used for signing this artifact and will be stored in public transparency logs and cannot be removed later.
Step #3: Error: signing /workspace/go/src/sigstore/fulcio/dist/fulcio-linux-ppc64le: getting key from Fulcio: verifying SCT: creating cached local store: resource temporarily unavailable
Step #3: main.go:62: error during command execution: signing /workspace/go/src/sigstore/fulcio/dist/fulcio-linux-ppc64le: getting key from Fulcio: verifying SCT: creating cached local store: resource temporarily unavailable
Step #3: 

saw a similar issue sometime ago and defining the TUF_ROOT seems to fix the issue