Extern: Update TinyGLTF to include fix for CVE-2022-3008

The use of wordexp(3) permits arbitrary code execution from manually-crafted
glTF files. See https://github.com/syoyo/tinygltf/issues/368 for more details.
In practice this shouldn't be an issue for Blender since the GlTF data isn't
manually crafted but from the OpenXR runtime (a bit like a driver). But
updating the library to include the fix is not a big deal anyway.

Note that the warning that required the local modification is no longer present upstream since
  0bfcb4f49e

Pull Request: https://projects.blender.org/blender/blender/pulls/105536

extern/tinygltf/README.blender

@@ -1,6 +1,5 @@
 Project: TinyGLTF
 URL: https://github.com/syoyo/tinygltf
 License: MIT
-Upstream version: 2.5.0, 19a41d20ec0
-Local modifications: 
-* Silence "enum value not handled in switch" warnings due to JSON dependency.
+Upstream version: 2.8.3, 84a83d39f55d
+Local modifications: None