fix(ci): set a network env variable to be used in `get-available-disks` (#4477)

* fix(ci): set a network env variable to be used in `get-available-disks`

* docs(ci): improve comment

.github/workflows/continous-integration-docker.yml

@@ -64,6 +64,8 @@ env:
   # TODO: use the output from ./.github/workflows/build-docker-image.yml
   IMAGE_NAME: zebrad-test
   GAR_BASE: us-docker.pkg.dev/zealous-zebra/zebra
+  # TODO: use environmental secrets for dynamic values
+  NETWORK: Mainnet
 
 jobs:
   get-available-disks:
@@ -91,6 +93,15 @@ jobs:
           service_account: 'github-service-account@zealous-zebra.iam.gserviceaccount.com'
           token_format: 'access_token'
 
+      # Disk images in GCP are required to be in lowercase, but the blockchain network
+      # uses sentence case, so we need to downcase ${{ env.NETWORK or github.event.inputs.network }}
+      #
+      # Passes a lowercase Network name to subsequent steps using $NETWORK env variable
+      - name: Downcase network name for disks
+        run: |
+          NETWORK_CAPS=${{ env.NETWORK || github.event.inputs.network }}
+          echo "NETWORK=${NETWORK_CAPS,,}" >> $GITHUB_ENV
+
       # Find a cached state disk for subsequent jobs needing a cached state without
       # restricting the result from any branch.
       #