Update mergify config for v3.1 backport label (#8814)

.mergify.yml

@@ -104,9 +104,9 @@ pull_request_rules:
           - automerge
       comment:
         message: automerge label removed due to a CI failure
-  - name: v2.3 feature-gate backport
+  - name: v3.0 feature-gate backport
     conditions:
-      - label=v2.3
+      - label=v3.0
       - label=feature-gate
     actions:
       backport:
@@ -117,10 +117,10 @@ pull_request_rules:
         labels:
           - feature-gate
         branches:
-          - v2.3
-  - name: v2.3 non-feature-gate backport
+          - v3.0
+  - name: v3.0 non-feature-gate backport
     conditions:
-      - label=v2.3
+      - label=v3.0
       - label!=feature-gate
     actions:
       backport:
@@ -128,10 +128,10 @@ pull_request_rules:
         title: "{{ destination_branch }}: {{ title }} (backport of #{{ number }})"
         ignore_conflicts: true
         branches:
-          - v2.3
-  - name: v2.3 backport warning comment
+          - v3.0
+  - name: v3.0 backport warning comment
     conditions:
-      - label=v2.3
+      - label=v3.0
     actions:
       comment:
         message: >
@@ -142,9 +142,9 @@ pull_request_rules:
           refactoring, plumbing, cleanup, etc that are not strictly
           necessary to achieve the goal. Any of the latter should go only
           into master and ride the normal stabilization schedule.
-  - name: v3.0 feature-gate backport
+  - name: v3.1 feature-gate backport
     conditions:
-      - label=v3.0
+      - label=v3.1
       - label=feature-gate
     actions:
       backport:
@@ -154,10 +154,10 @@ pull_request_rules:
         labels:
           - feature-gate
         branches:
-          - v3.0
-  - name: v3.0 non-feature-gate backport
+          - v3.1
+  - name: v3.1 non-feature-gate backport
     conditions:
-      - label=v3.0
+      - label=v3.1
       - label!=feature-gate
     actions:
       backport:
@@ -165,10 +165,10 @@ pull_request_rules:
         title: "{{ destination_branch }}: {{ title }} (backport of #{{ number }})"
         ignore_conflicts: true
         branches:
-          - v3.0
-  - name: v3.0 backport warning comment
+          - v3.1
+  - name: v3.1 backport warning comment
     conditions:
-      - label=v3.0
+      - label=v3.1
     actions:
       comment:
         message: >