Fix Cosmos enum discriminator casting by using GetValueComparer instead of GetProviderValueComparer

Co-authored-by: AndriySvyryd <6539701+AndriySvyryd@users.noreply.github.com>

Author: Copilot

src/EFCore.Cosmos/Query/Internal/CosmosReadItemAndPartitionKeysExtractor.cs

@@ -271,18 +271,12 @@ void ProcessPropertyComparison(string propertyName, SqlExpression propertyValue,
             if (propertyName == _discriminatorJsonPropertyName
                 && propertyValue is SqlConstantExpression { Value: { } specifiedDiscriminatorValue }
                 && _entityType.FindDiscriminatorProperty() is { } discriminatorProperty
-                && _entityType.GetDiscriminatorValue() is { } entityDiscriminatorValue)
+                && _entityType.GetDiscriminatorValue() is { } entityDiscriminatorValue
+                && discriminatorProperty.GetValueComparer().Equals(specifiedDiscriminatorValue, entityDiscriminatorValue))
             {
-                // Convert the specified discriminator value to provider value for comparison if there's a value converter
-                var convertedSpecifiedValue = discriminatorProperty.GetValueConverter()?.ConvertToProvider(specifiedDiscriminatorValue) 
-                    ?? specifiedDiscriminatorValue;
-                
-                if (discriminatorProperty.GetProviderValueComparer().Equals(convertedSpecifiedValue, entityDiscriminatorValue))
-                {
-                    // This is the case where there is a single leaf node with a discriminator value. We always know this value,
-                    // so the query never needs to drop out of ReadItem because of it.
-                    isCompatibleComparisonForReadItem = true;
-                }
+                // This is the case where there is a single leaf node with a discriminator value. We always know this value,
+                // so the query never needs to drop out of ReadItem because of it.
+                isCompatibleComparisonForReadItem = true;
             }
             else
             {