[core] Add Test Setup for Deno (#97)

This commit uses the "Continuous Integration" GitHub Action, to run
tests for the Deno code, which is used by the Supabase functions and our
Docker containers.

This commit also adds a first test so that the `deno test` command does
not fail.

.github/workflows/continuous-integration.yaml

@@ -34,3 +34,20 @@ jobs:
       - name: Test
         run: |
           flutter test
+
+  deno:
+    name: Deno
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Deno
+        uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+
+      - name: Test
+        run: |
+          deno test --import-map=supabase/functions/import_map.json supabase/functions