Add v1.5 and v1.6 backport support

.mergify.yml

@@ -50,14 +50,6 @@ pull_request_rules:
       label:
         add:
           - automerge
-  - name: v1.2 backport
-    conditions:
-      - label=v1.2
-    actions:
-      backport:
-        ignore_conflicts: true
-        branches:
-          - v1.2
   - name: v1.3 backport
     conditions:
       - label=v1.3
@@ -74,3 +66,19 @@ pull_request_rules:
         ignore_conflicts: true
         branches:
           - v1.4
+  - name: v1.5 backport
+    conditions:
+      - label=v1.5
+    actions:
+      backport:
+        ignore_conflicts: true
+        branches:
+          - v1.5
+  - name: v1.6 backport
+    conditions:
+      - label=v1.6
+    actions:
+      backport:
+        ignore_conflicts: true
+        branches:
+          - v1.6