build: remove defaults for create-release-proposal

To prevent users from executing the workflow via CLI
without passing the desired inputs.

PR-URL: #56042
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

.github/workflows/create-release-proposal.yml

@@ -11,12 +11,10 @@ on:
       release-line:
         required: true
         type: number
-        default: 23
         description: 'The release line (without dots or prefix). e.g: 22'
       release-date:
         required: true
         type: string
-        default: YYYY-MM-DD
         description: The release date in YYYY-MM-DD format
 
 concurrency: ${{ github.workflow }}