Set TKN_BINARY_URL in Makefile

[chmouel]

To make it easier to override the TKN_BINARY_URL, set it in the Makefile

Changes

Submitter Checklist

• 📝 A good commit message is important for other reviewers to understand the context of your change. Please refer to How to Write a Git Commit Message for more details how to write beautiful commit messages. We rather have the commit message in the PR body and the commit message instead of an external website.
• ♽ Run make test before submitting a PR (ie: with pre-commit, no need to waste CPU cycle on CI. (or even better install pre-commit and do pre-commit install in the root of this repo).
• ✨ We heavily rely on linters to get our code clean and consistent, please ensure that you have run make lint before submitting a PR. The markdownlint error can get usually fixed by running make fix-markdownlint (make sure it's installed first)
• 📖 If you are adding a user facing feature or make a change of the behavior, please verify that you have documented it
• 🧪 100% coverage is not a target but most of the time we would rather have a unit test if you make a code change.
• 🎁 If that's something that is possible to do please ensure to check if we can add a e2e test.
• 🔎 If there is a flakiness in the CI tests then don't necessary ignore it, better get the flakyness fixed before merging or if that's not possible there is a good reason to bypass it. (token rate limitation may be a good reason to skip).

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