ci(internal): update CI checks to test new internal subpackage

Cutting over to Cobra required moving the formerely 'main' package functions into an 'internal' subpackage, this updates the CI checks to run tests in there as well.

.github/workflows/ci.yml

@@ -15,8 +15,10 @@ jobs:
         uses: actions/[email protected]
         with:
           go-version: ">=1.22.1"
-      - name: Run main tests
-        run: go test
+      - name: Run `internal` tests
+        run: |
+          cd internal
+          go test
       - name: Run `sourcerer` tests
         run: |
           cd sourcerer