ci: trigger check workflows on merge_group for merge queue (#516)

Merge queues run required checks on the merge_group event; a workflow
without that trigger never reports, so the queue would stall exactly the
way path-filtered required checks stalled PRs (#507's lesson). CodeQL
runs default setup, which handles merge groups natively.

Author: creatornader

.github/workflows/ci.yml

@@ -1,6 +1,7 @@
 name: CI
 
 on:
+  merge_group:
   push:
     branches: [main]
   pull_request:

.github/workflows/python-sdk.yml

@@ -9,6 +9,7 @@ name: Python SDK conformance and cross-impl determinism
 # (D136). Path-scoped to the byte-identity surface.
 
 on:
+  merge_group:
   push:
     paths:
       - 'python/**'

.github/workflows/security-scan.yml

@@ -18,6 +18,7 @@ name: security-scan
 # unchanged by this workflow.
 
 on:
+  merge_group:
   push:
     branches: [main]
   pull_request: