Update test cases to use standard extension format

The Substrait tests cases under https://github.com/substrait-io/substrait/tree/main/tests/cases define an inclusion mechanism that has the general format of
```
### SUBSTRAIT_INCLUDE: '/extensions/<file>.yaml'
```

We should update this to just be the canonical urn format that was introduce in https://github.com/substrait-io/substrait/pull/859