Caching: Don't remove null values from hybrid cache to avoid broken content references repeatedly requiring a database hit (closes #18892) (#20209)

* Implement initial fix

* Revert "Implement initial fix"

This reverts commit 05e5803ebaa6330979e9a4ff6a4b343e74957ca0.

* Don't remove null cache values, they can always get removed when clearing cache

src/Umbraco.PublishedCache.HybridCache/Services/DocumentCacheService.cs

@@ -132,10 +132,8 @@ internal sealed class DocumentCacheService : IDocumentCacheService
             GetEntryOptions(key, preview),
             GenerateTags(key));
 
-        // We don't want to cache removed items, this may cause issues if the L2 serializer changes.
         if (contentCacheNode is null)
         {
-            await _hybridCache.RemoveAsync(cacheKey);
             return null;
         }