Upgrade to github-changelog-generator 0.0.4

Closes gh-23965

Author: snicoll

ci/tasks/generate-changelog.yml

@@ -4,7 +4,7 @@ image_resource:
   type: docker-image
   source:
     repository: springio/github-changelog-generator
-    tag: '0.0.3'
+    tag: '0.0.4'
 inputs:
 - name: git-repo
 - name: version