update CHANGELOG

CHANGELOG.md

@@ -2,7 +2,9 @@
 
 BACKWARDS INCOMPATIBILITIES:
 
- * `connection/ssh`: The `agent` field now defaults to `true` if
+ * command/push: If a variable is already set within Atlas, it won't be
+     updated unless the `-overwrite` flag is present [GH-2373]
+ * connection/ssh: The `agent` field now defaults to `true` if
      the `SSH_AGENT_SOCK` environment variable is present. In other words,
      `ssh-agent` support is now opt-out instead of opt-in functionality. [GH-2408]
  * `concat()` has been repurposed to combine lists instead of strings (old behavior