fix(ci): pipe COINBASE_ONRAMP_API_KEY into local.properties

The workflow never wrote the Coinbase onramp API key to
local.properties, so production builds shipped with an empty string
and the server rejected GetJwtRequest with:

    INVALID_ARGUMENT: invalid ApiKey.Value: value length must be 36 runes

Author: bmc08gt

.github/workflows/build-fcash2-upload-android.yml

@@ -94,6 +94,9 @@ jobs:
       - name: Setup Mixpanel API Key
         run: echo MIXPANEL_API_KEY=\"${{ secrets.FLIPCASH_MIXPANEL_API_KEY }}\" >> ./local.properties
 
+      - name: Setup Coinbase OnRamp API Key
+        run: echo COINBASE_ONRAMP_API_KEY=${{ secrets.COINBASE_ONRAMP_API_KEY }} >> ./local.properties
+
       - name: Run tests
         run: bundle exec fastlane android flipcash_tests