Use asdf plugin names in tests, and in specific, fix opentofu parsing in asdf parser

[tspearconquest]

This PR should fix opentofu parsing in asdf parser. The asdf .tool-versions file uses the plugin name. For opentofu, the plugin is named "opentofu" rather than "tofu" so we must stick to the convention already in-use.

Additionally, it seemed silly to have asdf parsing tests for tenv to be checking asdf plugins which aren't related to the requested feature which brought about this code and the bug. So I've updated the tests and test data to use tenv tools only: atmos, opentofu and terragrunt. I thought of adding a test for terraform as well but felt it was probably beyond the scope of this bugfix.

[dvaumoron]

thanks

[tspearconquest]

I made one minor mistake in the test data 1.8.6 instead of 1.8.7. Apologies, I am submitting that patch now.

[tspearconquest]

Oh I see it was fixed when you merged. Thanks for catching that!