Updates the Stan submodule to b5e23b2.

stan-buildbot · stan-buildbot · commit b8d22ba7c428 · 2020-08-29T02:29:19.000-04:00
diff --git a/stan b/stan
@@ -1 +1 @@
-Subproject commit 1abc0f3bae87843d26cd4b20f708cc78801ad02e
+Subproject commit b5e23b2d9b5b0944a9d3db7e75d94aa7888a096c
