Update python-slack-sdk to version 3.18.3 / rev 2 via SR 1008879
    
    https://build.opensuse.org/request/show/1008879
    by user mcalabkova + RBrownFactory
    - Update to version 3.18.3
      Changes
      * #1262 Fix #1261 blocks/attachments as str for chat. API calls should be clearly supported - Thanks @seratch
      * #1259 Fix #1258 Tuple value for blocks argument does not work for Web API calls - Thanks @tommasobertoni
      * #1253 Minor update: max elements in ActionsBlock to 25 - Thanks @YSaxon
      * #1249 #1251 Add in timezone property for timepicker element - Thanks @hello-ashleyintech