Actually, no, use GH variables instead of GH secrets

GH secrets are not accessible to workflows triggered by PRs from forks, which doesn't work with how we work. Lets use variables instead, with the caveat that these are public now. Not a problem since we configured in such a way that they only work for Lynx contracts.

.github/workflows/lynx.yml

@@ -10,6 +10,10 @@ on:
       - epic-*
   workflow_dispatch:
 
+env:
+  DEMO_L1_PROVIDER_URI: ${{ vars.DEMO_L1_PROVIDER_URI }}
+  DEMO_L2_PROVIDER_URI: ${{ vars.DEMO_L2_PROVIDER_URI }}
+
 jobs:
   python-tests:
 
@@ -51,7 +55,4 @@ jobs:
         run: python -c "import nucypher; print(nucypher.__version__)"
 
       - name: Lynx testnet script
-        env:
-          DEMO_L1_PROVIDER_URI: ${{ secrets.DEMO_L1_PROVIDER_URI }}
-          DEMO_L2_PROVIDER_URI: ${{ secrets.DEMO_L2_PROVIDER_URI }}
         run: python examples/testnet_simple_taco.py