Add CI action for validation of native shaders

.github/workflows/validation.yml

@@ -0,0 +1,16 @@
+name: validation
+on:
+  pull_request:
+    paths:
+    - 'tests/snapshots/*.snap'
+
+jobs:
+  linux:
+    name: SPIR-V and GLSL
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install tools
+        run: sudo apt-get install spirv-tools glslang-tools
+      - run: make validate-spv
+      - run: make validate-glsl