[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

@@ -2,6 +2,7 @@
 # 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: