ci: Fix version for ajv-cli validator

New major release doesn't support many formats anymore and must be configured with external plugins.
Just stick with the old version, we don't need new fancy features for now.

Author: zehnm

.github/workflows/validate_config.yml

@@ -18,7 +18,7 @@ jobs:
     - uses: actions/setup-node@v1
       with:
         node-version: '10.x'
-    - run: npm install -g ajv-cli
+    - run: npm install -g ajv-cli@3.3.0
     - run: ajv validate -s config-schema.json  -d config.json
     - run: ajv validate -s hardware-schema.json  -d hardware.json
-    
+