[renovate] Update renovate/renovate Docker tag to v38.18.17

See merge request !991

Co-authored-by: Fabian Seidl <fabian.seidl@h-da.de>
Co-authored-by: Neil Schark <neil.schark@h-da.de>
Co-authored-by: Renovate Bot <renovate@danet.fbi.h-da.de>

.gitlab/ci/.renovate.yml

 renovate:
     stage: tools
 
-    image: renovate/renovate:38.18.12
+    image: renovate/renovate:38.18.17
 
     variables:
         LOG_LEVEL: debug