Fix recipe

Author: VeckoTheGecko

.github/ci/recipe.yaml

@@ -4,7 +4,7 @@
 # Adapted from the conda forge recipe
 context:
   name: parcels
-  version: ${{ env['PARCELS_ALPHA_VERSION'] }}
+  version: ${{ env.get('PARCELS_ALPHA_VERSION') }}
 
 package:
   name: ${{ name|lower }}