Add changelog entry

Author: solrbot

changelog/unreleased/PR#3122-update-adobe-testing-s3mock.yml

@@ -0,0 +1,7 @@
+title: Update adobe.testing.s3mock to v4
+type: dependency_update
+authors:
+- name: solrbot
+links:
+- name: PR#3122
+  url: https://github.com/apache/solr/pull/3122