fix: Improve validation errors

test-files/schema/modules/signing-v1.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "/modules/signing.json",
+  "type": "object",
+  "properties": {
+    "type": {
+      "type": "string",
+      "const": "signing",
+      "description": "The signing module is used to install the required signing policies for cosign image verification with rpm-ostree and bootc.\nhttps://blue-build.org/reference/modules/signing/"
+    },
+    "no-cache": {
+      "type": "boolean",
+      "default": false,
+      "description": "Whether to disabling caching for this layer.\nhttps://blue-build.org/reference/module/#no-cache-optional"
+    }
+  },
+  "required": [
+    "type"
+  ],
+  "additionalProperties": false
+}