Uploading changeset specs fails with "failed to normalize JSON: yaml: control characters are not allowed"

Created by: mrnugget

Campaign spec:

name: remove-node-modules
description: node modules fun

on:
  - repositoriesMatchingQuery: repo:automation-testing count:1

steps:
  - run: yarn add @angular/cli
    container: node:14.8

changesetTemplate:
  # [...]

that crashes src-cli with the following error:

⠧  Sending changeset specs

❌ Error:
   GraphQL errors: 1 error occurred:
        * {
     "message": "failed to normalize JSON: yaml: control characters are not allowed",
     "path": [
       "createChangesetSpec"
     ]
   }