ci: Build libOBS with MSVC on Windows

obs-studio does not yet support ClangCL, resulting in a broken build. We don't want to check if obs-studio is broken, we only want to check if StreamFX is broken.

.github/workflows/main.yml

@@ -111,6 +111,9 @@ jobs:
     - name: "Dependency: OBS Libraries"
       id: obs
       if: ${{ steps.obs-cache.outputs.cache-hit != 'true' }}
+      env:
+        # obs-studio does not support ClangCL
+        CMAKE_GENERATOR_TOOLSET: ""
       shell: bash
       run: |
         # Apply patches to obs-studio