Skip online metadata fetch in BackgroundDataStoreProcessor during tests

This prevents flaky network requests and timeouts in unit tests that involve the BackgroundDataStoreProcessor (e.g. BackgroundDataStoreProcessorTests). The `backpopulateUserTags` task was attempting to download the full `online.db` database, causing significant delays and potential failures in CI environments.

Skipping this operation when `DebugUtils.IsNUnitRunning` is true ensures tests run reliably and quickly without external dependencies.

Co-authored-by: winnerspiros <1675249+winnerspiros@users.noreply.github.com>

Author: google-labs-jules[bot]

osu.Game/Database/BackgroundDataStoreProcessor.cs

@@ -10,6 +10,7 @@
 using Newtonsoft.Json;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Development;
 using osu.Framework.Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Logging;
@@ -636,6 +637,8 @@ private void backpopulateUserTags()
         {
             if (!localMetadataSource.Available || !localMetadataSource.IsAtLeastVersion(3))
             {
+                if (DebugUtils.IsNUnitRunning) return;
+
                 Logger.Log(@"Local metadata cache has too low version to backpopulate user tags, attempting refetch...");
                 localMetadataSource.FetchCache().WaitSafely();