tests : conditional python & node json schema tests (#6207)

* json: only attempt python & node schema conversion tests if their bins are present

Tests introduced in https://github.com/ggerganov/llama.cpp/pull/5978
disabled in https://github.com/ggerganov/llama.cpp/pull/6198

* json: orange warnings when tests skipped

* json: ensure py/js schema conv tested on ubuntu-focal-make

* json: print env vars in test

.github/workflows/build.yml

@@ -135,6 +135,9 @@ jobs:
 
   ubuntu-focal-make:
     runs-on: ubuntu-20.04
+    env:
+      LLAMA_NODE_AVAILABLE: true
+      LLAMA_PYTHON_AVAILABLE: true
 
     steps:
       - name: Clone
@@ -147,6 +150,14 @@ jobs:
           sudo apt-get update
           sudo apt-get install build-essential gcc-8
 
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.11"
+
       - name: Build
         id: make_build
         env: