Indicate dry_run to be of type boolean

This is so it gets rendered as a checkbox. We'll default it to `true` to avoid accidental releases.

Author: jamis

.github/workflows/release.yml

@@ -5,9 +5,10 @@ on:
   workflow_dispatch:
     inputs:
       dry_run:
-        description: Whether this is a dry run or not ("false" to deploy)
+        description: Whether this is a dry run or not
         required: true
-        type: string
+        default: true
+        type: boolean
 
 env:
   SILK_ASSET_GROUP: mongodb-ruby-driver