Add branch-scoped push trigger to probe workflow

Lets Phase 0 be tested directly off the feature branch (no merge to main / PR approval needed); environment: cicd still yields OIDC subject repo:github/copilot-sdk:environment:cicd.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

.github/workflows/canary-feed-oidc-probe.yml

@@ -5,6 +5,8 @@ name: canary-feed-oidc-probe
 # the internal copilot-canary-spike npm feed. Delete once Phase 0 is proven.
 
 on:
+  push:
+    branches: [mackinnonbuck-canary-oidc-probe]
   workflow_dispatch:
 
 permissions: