fix: add timestep stamp to generating rootfs (#130)

Issue #, if available:

*Description of changes:*

fix issue in setting timestamp label


*Testing done:*


- [x] I've reviewed the guidance in CONTRIBUTING.md


#### License Acceptance

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Signed-off-by: Gavin Inglis <[email protected]>

.github/workflows/rootfs.yaml

@@ -21,6 +21,9 @@ jobs:
       matrix:
         arch: ['amd64', 'arm64']
     steps:
+      - name: Generate Timestamp
+        id: timestamp
+        run: echo "::set-output name=value::$(date +%s)"
       - name: configure aws credentials
         uses: aws-actions/configure-aws-credentials@v2
         with: