Mark 3.1.56 as released (#21518)

Author: aheejin

ChangeLog.md

@@ -18,8 +18,11 @@ to browse the changes between the tags.
 
 See docs/process.md for more on how version tagging works.
 
-3.1.56 (in development)
+3.1.57 (in development)
 -----------------------
+
+3.1.56 - 03/13/24
+-----------------
 - emscripten will now generate an `unused-command-line-argument` warning if
   a `-s` setting is specified more than once on the command line with
   conflicting values.  In this case the first setting is ignored. (#21464)

emscripten-version.txt

@@ -1 +1 @@
-3.1.56-git
+3.1.57-git