In generate-screenshots workflow, use commit action for generating signing commits

[angusbayley]

Ticket here

Uses the ghcommit action to make a verified commit for the generated screenshots.

In this PR we replace our manual git commands for creating a commit with the ghcommit action, which makes a request to the Github API to create a commit instead. In this PR we use that action, but provide the GITHUB_TOKEN to authenticate the request. The GITHUB_TOKEN is locally scoped to just that workflow run (i.e. short lived), and is generated by Github. When Github receives the request it parses the GITHUB_TOKEN and recognises the commit as originating from the repo's own actions, marking it as Verified on this basis. Verification that the commit is generated within the repo's actions is sufficient because 3rd parties (people outside the Ledger organisation) cannot initiate a generate-screenshots run.

Test PR for this is #8806, with the workflow run here. 🟢, commit generated and verified ✅

---

During this work 2 other approaches were tried

1. using swinton/commit, suggested in this comment. Contrary to that comment, that action is not implemented anywhere in the earn repo. I tried this action and it works fine for single-file commits but it doesn't have a documented way of adding multiple files simultaneously. It's a single-developer effort (perhaps explains the lack of support for common use cases) and isn't actively maintained. Even if I had found a hack for adding multiple files I wasn't comfortable introducing this to the team - not clean enough, high risk of it being hard to work with in the future
2. using GPG encryption with live-github-bot's credentials. This didn't work because live-github-bot's email address contains [ and ] characters, which GPG does not recognise as valid characters in an email address

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

4 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
ledger-live-github-bot	⬜️ Ignored (Inspect)	Visit Preview		Jan 6, 2025 10:27am
native-ui-storybook	⬜️ Ignored (Inspect)	Visit Preview		Jan 6, 2025 10:27am
react-ui-storybook	⬜️ Ignored (Inspect)	Visit Preview		Jan 6, 2025 10:27am
web-tools	⬜️ Ignored (Inspect)	Visit Preview		Jan 6, 2025 10:27am

[github-actions]

There as been no activity on this PR for the last 14 days. Please consider closing this PR.

[themooneer]

LGTM