build: recommend Xcode 13 or later

Change-Id: I463862ef11ad132e47e393007a449e942d293334
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7029313..65e90ce 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,6 +1,8 @@
 name: CI
 on:
   push:
+    branches:
+      - '**'
     paths-ignore:
       - 'Dockerfile'
       - '.dockerignore'