CI: Propagated error code when glue generation fails

This used to be ignored as we ran the X11 version with Vulkan software renderer and xvfb-run, which could crash at the time. Now that we have headless mode, this is not a problem anymore.

.github/workflows/linux_builds.yml

@@ -130,7 +130,7 @@ jobs:
       - name: Generate C# glue
         if: ${{ matrix.build-mono }}
         run: |
-          ${{ matrix.bin }} --headless --generate-mono-glue ./modules/mono/glue || true
+          ${{ matrix.bin }} --headless --generate-mono-glue ./modules/mono/glue
 
       - name: Build .NET solutions
         if: ${{ matrix.build-mono }}