[CI] Disable backward compatibility check

At the moment, we have no history to diff against, resulting in an error

> Error loading nodes: Could not find __init__.py in base_repo

This commit should be reverted once the initial node implementation has
been merged to main.

Signed-off-by: David Feltell <david.feltell@foundry.com>

.github/workflows/validate.yml.disabled

@@ -0,0 +1,18 @@
+# openassetio-comfyui
+# Copyright (c) 2025 The Foundry Visionmongers Ltd
+# SPDX-License-Identifier: Apache-2.0
+
+# TODO(DF): Re-enable once initial PR merged to set a baseline.
+name: Validate backwards compatibility
+
+on:
+  pull_request:
+    branches:
+      - master
+      - main
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: comfy-org/node-diff@main