fix: disable async file IO on WebGL

Author: vaind

src/Sentry.Unity/WebGL/SentryWebGL.cs

@@ -43,6 +43,9 @@ public static void Configure(SentryUnityOptions options)
             //     Please contact Customer Support with a sample project so that we can reproduce the problem and troubleshoot it."
             // Maybe we could write a file when this error occurs and recognize it on the next start. Like unity-native.
             options.CrashedLastRun = () => false;
+
+            // Disable async when accessing files (e.g. FileStream(useAsync: true)) because it throws on WebGL.
+            options.UseAsyncFileIO = false;
         }
     }