update references

Author: deusebio

docs/reference/releases/index.md

@@ -10,12 +10,12 @@ myst:
 Charmed Apache Spark has the following stable revisions:
 
 * [2](reference-releases-revision-2)
-* [3](reference-releases-revision-3)
+* [4](reference-releases-revision-4)
 
 ```{toctree}
 :titlesonly:
 :hidden:
 
 Revision 2<revision-2.md>
-Revision 3<revision-3.md>
+Revision 4<revision-4.md>
 ```