chore: change the required PR approving number to 2 (#463)

diff --git a/.asf.yaml b/.asf.yaml
index cef24c5..784c5c2 100644
--- a/.asf.yaml
+++ b/.asf.yaml
@@ -34,6 +34,10 @@
       squash:  true
       merge:   false
       rebase:  false
+    protected_branches:
+      master:
+        required_pull_request_reviews:
+          required_approving_review_count: 2
 
 notifications:
     commits:      notifications@apisix.apache.org