Only use valid characters in dummy AWS access keys

[lpsinger]

Only use letters and numbers in dummy AWS access keys. Access keys that contain underscores are invalid.

This is required for using Architect with DynamoDB Local.

See notes section of https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBLocal.DownloadingAndRunning.html.

Thank you for helping out! ✨

We really appreciate your commitment to improving Architect

To maintain a high standard of quality in our releases, before merging every pull request we ask that you've completed the following:

• [ ] Forked the repo and created your branch from main
• [ ] Made sure tests pass (run npm it from the repo root)
• [ ] Expanded test coverage related to your changes:
  • [ ] Added and/or updated unit tests (if appropriate)
  • [ ] Added and/or updated integration tests (if appropriate)
• [ ] Updated relevant documentation:
  • [ ] Internal to this repo (e.g. readme.md, help docs, inline docs & comments, etc.)
  • [ ] Architect docs (arc.codes)
• [ ] Summarized your changes in changelog.md
• [ ] Linked to any related issues, PRs, etc. below that may relate to, consume, or necessitate these changes

Please also be sure to completed the CLA (if you haven't already).

Learn more about contributing to Architect here.

Thanks again!

[lpsinger]

CI failures look like they are probably unrelated.

[filmaj]

Hey thanks for the PR! I think the build is failing in this project at the moment, but I think there is a fix on the way in #736.