update mysql docker tag to v8.3 (PR solidnerd#461)

Author: HJF9w

docker-compose.test.yml

@@ -6,7 +6,7 @@ services:
     depends_on:
     - bookstack
   mysql:
-    image: mysql:8.2
+    image: mysql:8.3
     environment:
     - MYSQL_ROOT_PASSWORD=secret
     - MYSQL_DATABASE=bookstack

docker-compose.yml

@@ -2,7 +2,7 @@
 version: '3'
 services:
   mysql:
-    image: mysql:8.2
+    image: mysql:8.3
     environment:
     - MYSQL_ALLOW_EMPTY_PASSWORD=1
     - MYSQL_DATABASE=bookstack