Fix ember-test-selectors custom adapter for 6.x

[mydea]

The 6.x release of ember-test-selectors dropped the attribute binding for classic components. This leads to a build error due to the current compat-adapter of embroider:

module not found: Error: 
Can't resolve '../node_modules/ember-test-selectors/utils/bind-data-test-attributes' 
in '$TMPDIR/embroider/d7920e/assets/my-app.js'

This PR makes the compat adapter only run for ember-test-selector versions below 6. Not sure if there is a "nicer" way to check this than to take the version of the addon pkg info, but I guess it works well enough for this case!

[thoov]

We can leverage shouldApplyAdapter (#772) which will completely ignore the adapter altogether. An example of this is: https://github.com/embroider-build/embroider/pull/900/files

[mydea]

Ah, nice! I rewrote it to leverage that.