Update stan submodule

hsbadr · hsbadr · commit 3a94f4a1a8fd · 2024-01-19T11:51:28.000-05:00
diff --git a/StanHeaders/inst/include/upstream b/StanHeaders/inst/include/upstream
@@ -1 +1 @@
-Subproject commit 979e7a61b84b101f064185c1d8204b92c31f74ad
+Subproject commit dd48b6733cc666b8c3297e46b7f53947d41a6758
