fix: correct subscription from StdOut to StdErr in UpdatePackageListAsyncMethodTests

Author: WolfBublitz

tests/PackageManagerTests/AptPackageManagerTests/src/MethodTests/UpdatePackageListAsyncMethodTests.cs

@@ -16,7 +16,7 @@ public async Task ShouldUpdatePackageListSuccessfully(CancellationToken cancella
         // Arrange
         List<string> stdOut = [];
         AptPackageManager packageManager = new();
-        packageManager.StdOut.Subscribe(stdOut.Add);
+        packageManager.StdErr.Subscribe(stdOut.Add);
 
         // Act
         await packageManager.UpdatePackageListAsync(cancellationToken).ConfigureAwait(false);