add != to Mat2D

fissioned from https://github.com/rive-app/rive/pull/4186

Diffs=
59ecc6712 Add != operator

.rive_head

diff --git a/.rive_head b/.rive_head
index 4a69d7f..b4cd9d5 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-ed84a5ca3153d142172d258bda071a98de3dd0e7
+59ecc6712369bd7c160c35bbb263a36771155923

include/rive/math/mat2d.hpp

diff --git a/include/rive/math/mat2d.hpp b/include/rive/math/mat2d.hpp
index d1c3a63..02f20f1 100644
--- a/include/rive/math/mat2d.hpp
+++ b/include/rive/math/mat2d.hpp
@@ -78,5 +78,8 @@
     return a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3] && a[4] == b[4] &&
            a[5] == b[5];
 }
+
+inline bool operator!=(const Mat2D& a, const Mat2D& b) { return !(a == b); }
+
 } // namespace rive
 #endif