Update buildspec to newest obs-studio commit

This is required to fix Windows build issues on GitHub Actions due to
changed behavior of CMake 3.24.

buildspec.json

@@ -4,7 +4,7 @@
             "version": "28.0.0-beta1",
             "repository": "https://github.com/obsproject/obs-studio.git",
             "branch": "master",
-            "hash": "67f7a84076be2c73d172eb14265c60d6209598db"
+            "hash": "43a49dca47344a5170159ef99b86b97f90d4e4ad"
         },
         "prebuilt": {
             "version": "2022-08-02",