chore: point screens-dev-green at api-dev-blue

While mbta/devops#2122 updates the `API_V3_URL`
for screens-dev-green to point to api-dev-blue, we don't use that value
if `ENVIRONMENT_NAME` is set.

This updates the API url used when `ENVIRONMENT_NAME` is
`"screens-dev-green"` to point to api-dev-blue.

config/runtime.exs

@@ -10,7 +10,7 @@ api_v3_url =
   case eb_env_name do
     "screens-prod" -> "https://api-v3.mbta.com/"
     "screens-dev" -> "https://api-dev.mbtace.com/"
-    "screens-dev-green" -> "https://api-dev-green.mbtace.com/"
+    "screens-dev-green" -> "https://api-dev-blue.mbtace.com/"
     _ -> System.get_env("API_V3_URL", "https://api-v3.mbta.com/")
   end