Timer trigger sample fails to resolve import

[itowlson]

As part of ongoing component and Wasmtime infrastructure improvements, the examples/spin-timer trigger sample was updated in #1615 to refer to the Spin config API in a new way. Unfortunately, although both the trigger and example guest build okay, the example guest fails at spin up with:

$ spin up
Error: Failed to instantiate component 'three'

Caused by:
    0: Failed to instantiate component 'three'
    1: import `fermyon:example/config` has the wrong type
    2: instance export `get-config` has the wrong type
    3: expected func found nothing

I am not sure how to go about fixing this. @rylev @dicej do you have any ideas please? I'm not sure how to share the diff in a text format so here's ye olde GitHub screenshot:

The workaround is to revert the sample to an earlier commit (Spin itself doesn't need to be reverted as the trigger is an independent process).

Incidentally, this highlights a gap in CI - it tests that the sample builds, but doesn't test that it loads and runs - it would be good to improve our coverage here.