Avoid redundant SourceRepository allocation on cache hit in CachingSourceProvider (#7132)

Author: nareshjo

src/NuGet.Core/NuGet.Protocol/CachingSourceProvider.cs

@@ -64,6 +64,11 @@ public SourceRepository CreateRepository(PackageSource source)
 
         public SourceRepository CreateRepository(PackageSource source, FeedType type)
         {
+            if (_cachedSources.TryGetValue(source.Source, out SourceRepository cached))
+            {
+                return cached;
+            }
+
             return _cachedSources.GetOrAdd(source.Source, new SourceRepository(source, _resourceProviders, type));
         }