Add missing GITHUB_TOKEN to docker image push action.

Without this the get_release_info action is failing
as it doesn't have access to the github token that
gives it access to repository metadata.

Author: NlightNFotis

.github/workflows/release-packages.yaml

@@ -210,6 +210,8 @@ jobs:
 
   push-docker-image-dockerhub:
     runs-on: ubuntu-20.04
+    env:
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
       - name: Checkout CBMC source
         uses: actions/checkout@v2