fix: update faucet link r/demo/boards

[waymobetta]

The faucet link was pointing to a resource that is no longer available. The new link points to the faucet on staging (testnet; test3).

Checklists...

Contributors Checklist

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

Maintainers Checklist

• Checked that the author followed the guidelines in CONTRIBUTING.md
• Checked the conventional-commit (especially PR title and verb, presence of BREAKING CHANGE: in the body)
• Ensured that this PR is not a significant change or confirmed that the review/consideration process was appropriate for the change