Maintenance: Sync the database preflight check versions with what is actually required.

lib/zammad/application/initializer/db_preflight_check/mysql2.rb

@@ -66,9 +66,9 @@ module Zammad
           def self.min_version
             case vendor
             when 'MySQL'
-              '5.6'
+              '5.7'
             when 'MariaDB'
-              '10.0'
+              '10.3'
             end
           end
 

lib/zammad/application/initializer/db_preflight_check/postgresql.rb

@@ -58,7 +58,7 @@ module Zammad
           end
 
           def self.min_version
-            @min_version ||= '9.1'
+            @min_version ||= '9.3'
           end
 
           def self.vendor