pass in dafny version

Author: josecorella

.github/actions/mpl-head/action.yml

@@ -1,6 +1,10 @@
 name: "Check Out and update files with MPL-HEAD"
 description: "Updates the MPL submodule to point at HEAD and updates the files that depend on the version defined in project.properties"
 inputs:
+  dafny:
+    description: "The Dafny version to run"
+    required: true
+    type: string
   update-and-regenerate-mpl:
     description: "Locally update MPL to the tip of master and regenerate its code"
     required: true

.github/actions/mpl-head/mpl_head_codegen.yml

@@ -42,6 +42,7 @@ jobs:
       - uses: ./.github/actions/mpl-head
         if: ${{ inputs.mpl-head == true }}
         with:
+          dafny: ${{ env.DAFNY_VERSION }}
           update-and-regenerate-mpl: true
 
       # Only used to format generated code