chore(proto): scope gate cardinality break suppression inline

Move the FIELD_SAME_CARDINALITY exception from buf.yaml to
an inline ignore on PolicyAttachment.gate in crafting_schema.proto
limiting the suppression to the specific field change.

Signed-off-by: Matías Insaurralde <matias@chainloop.dev>

Author: matiasinsaurralde

app/controlplane/api/workflowcontract/v1/crafting_schema.proto

@@ -240,6 +240,7 @@ message PolicyAttachment {
   // - true: policy violations are blocking for this policy
   // - false: policy violations are non-blocking for this policy
   // - unset: inherit organization-level default behavior
+  // buf:breaking:ignore FIELD_SAME_CARDINALIT
   optional bool gate = 7;
 
   message MaterialSelector {