Fix for nested events in CPP

Fixes nested events not propagating up to the parent artboard due to a recent naming change from `artboard()` to `artboardInstance()`.

Diffs=
657f65e1c Fix for nested events in CPP (#7708)

Co-authored-by: Philip Chung <philterdesign@gmail.com>

.rive_head

diff --git a/.rive_head b/.rive_head
index 49e224c..75cf471 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-0a11e599f81bdff08afe8365b0e25115431eba8c
+657f65e1c0b0c63524c65e2b5e1fbe6459e1ae69

src/animation/state_machine_instance.cpp

diff --git a/src/animation/state_machine_instance.cpp b/src/animation/state_machine_instance.cpp
index 6f006f7..9bbe875 100644
--- a/src/animation/state_machine_instance.cpp
+++ b/src/animation/state_machine_instance.cpp
@@ -1089,7 +1089,8 @@
             {
                 for (const auto event : events)
                 {
-                    auto sourceArtboard = source == nullptr ? artboard() : source->artboard();
+                    auto sourceArtboard =
+                        source == nullptr ? artboard() : source->artboardInstance();
 
                     // listener->eventId() can point to an id from an event in the context of this
                     // artboard or the context of a nested artboard. Because those ids belong to