Add Tenderly Env vars to spell crafter checklist

[oddaf]

On the latest spell I spent quite a bit of time trying to use my Tenderly user ID in the env var TENDERLY_USER, when I should be using my team's ID instead. This PR updates the checklist to detail what goes in each of the ENV vars in a way similar to the deployment script section.

[SidestreamColdMelon]

I don't think checklist is a good place to store env variables and setup instructions:

• Setup only needs to happen once while every checklist item suppose to be followed every single time
• Code of the tenderly script lays in a different repository so it's harder to maintain two places in sync

Instead, you can link a readme section that already explains that:

Suggested change

	* Cast spell on a newly created Tenderly Testnet
	* [ ] `export TENDERLY_USER='<ORG_SLUG>'` (e.g.: dewiz-xyz)
	* [ ] `export TENDERLY_PROJECT='makerdao'`
	* [ ] `export TENDERLY_ACCESS_KEY='<ACCESS_KEY>'` (from the **account level**, not from the organization level)
	* Cast spell on a newly created Tenderly Testnet (see [setup instructions](https://github.com/makerdao/spells-mainnet?tab=readme-ov-file#cast-to-tenderly))

Alternatively, you can submit a PR into makerdao/spells-mainnet to move this setup instructions into a more visible place (eg inside relevant folder)

[DaiFoundation-DevOps]

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