Simplify testing situation to assure import and require works

[NullVoxPopuli]

Now we don't have duplication.

in a previous attempt

The only thing we need to remember is that we can't directly `require` or `import` in module-space in the tests themselves :sweat_smile: 

[ef4]

I don't think this is worth it. There's no reason to think the details of the API would be different between import and require. It's enough to write the tests one way (probably import) and then have a single test that does a require and invokes one of the functions to make sure it's really there.

[mansona]

I don't see the cjs test running in https://github.com/embroider-build/content-tag/actions/runs/7604656450/job/20707813134?pr=59 🤔

[NullVoxPopuli]

it's sorted