[renovate] Update renovate/renovate Docker tag to v38.18.4

This MR contains the following updates:

Package	Type	Update	Change
renovate/renovate (source)	image	minor	38.17.1 -> 38.18.4

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This MR has been generated by Renovate Bot.

.gitlab/ci/.renovate.yml

 renovate:
     stage: tools
 
-    image: renovate/renovate:38.17.1
+    image: renovate/renovate:38.18.4
 
     variables:
         LOG_LEVEL: debug