Update pingcap/pd Docker tag to v8.5.6

Author: renovate[bot]

ops/docker-compose/database/tidb/compose.yaml

@@ -8,7 +8,7 @@ x-network: &network
 services:
   pd0:
     <<: *network
-    image: pingcap/pd:v8.5.5
+    image: pingcap/pd:v8.5.6
     ports:
       - "2379"
     command:
@@ -25,7 +25,7 @@ services:
 
   pd1:
     <<: *network
-    image: pingcap/pd:v8.5.5
+    image: pingcap/pd:v8.5.6
     ports:
       - "2379"
     command:
@@ -42,7 +42,7 @@ services:
 
   pd2:
     <<: *network
-    image: pingcap/pd:v8.5.5
+    image: pingcap/pd:v8.5.6
     ports:
       - "2379"
     command: