Update 3.1.56's release date (#21537)

After #21518 landed, the previous 3.1.56 release
(emscripten-core/emsdk#1353) turned out to be
broken so we replaced 3.1.56 with the new one
(emscripten-core/emsdk#1360). So here to be
precise we update the date of the new 3.1.56 release.

Author: aheejin

ChangeLog.md

@@ -21,7 +21,7 @@ See docs/process.md for more on how version tagging works.
 3.1.57 (in development)
 -----------------------
 
-3.1.56 - 03/13/24
+3.1.56 - 03/14/24
 -----------------
 - emscripten will now generate an `unused-command-line-argument` warning if
   a `-s` setting is specified more than once on the command line with