Ignore Stainless Endpoint/NotFound for removed Plaid endpoints

The Plaid endpoints were removed from the spec in PR #304 but are still
referenced in the Stainless Studio config. Ignoring these diagnostics
prevents the preview build from failing until the Studio config is updated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: AaryamanBhute

.stainless/stainless.yml

@@ -684,3 +684,6 @@ diagnostics:
     Schema/EnumHasOneMember: true
     Schema/RequiredPropertyNotDefined: true
     Schema/IsAmbiguous: true
+    Endpoint/NotFound:
+      - post /plaid/link-tokens
+      - post /plaid/callback/{plaid_link_token}