Add a note that the most-recent version in ChangeLog.md is in development (#17576)

Author: dschuff

ChangeLog.md

@@ -18,7 +18,7 @@ to browse the changes between the tags.
 
 See docs/process.md for more on how version tagging works.
 
-3.1.19
+3.1.19 (in development)
 ------
 - Old method of metadata extraction via wasm-emscripten-finalize removed
   in favor of local python code. (#16529)