Fix ab-testing deploy workflows

[Jakeii]

What does this change?

Quite a few fixes to get the ab-testing deploy to actually work, not sure how this got past me in #14333 ...

• The secrets weren't being passed properly to the deploy workflow
• The calling of the reusable workflow wasn't quite right
• the build wasn't saved as an artifact to deploy in a later step

Successful deploy after these changes: https://github.com/guardian/dotcom-rendering/actions/runs/18343600883

[github-actions]

Deploy build 45631 of Mobile::mobile-apps-rendering to CODE

All deployment options

• Deploy build 45631 of Mobile::mobile-apps-rendering to CODE
• Deploy parts of build 45631 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.

[github-actions]

Deploy build 21391 of dotcom:rendering-all to CODE

All deployment options

• Deploy build 21391 of dotcom:rendering-all to CODE
• Deploy parts of build 21391 to CODE by previewing it first
• What's on CODE right now?

---

From guardian/actions-riff-raff.

[github-actions]

Hello 👋! When you're ready to run Chromatic, please apply the run_chromatic label to this PR.

You will need to reapply the label each time you want to run Chromatic.

Click here to see the Chromatic project.

[GHaberis]

Looks good 👍

[gu-prout]

Seen on PROD (merged by @Jakeii 7 minutes and 3 seconds ago) Please check your changes!