Bump System.Memory to 4.6.3 (#2498)

# Conflicts:
#	src/Confluent.Kafka/Confluent.Kafka.csproj

Author: Havret

src/Confluent.Kafka/Confluent.Kafka.csproj

@@ -31,7 +31,7 @@
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net462'">
-    <PackageReference Include="System.Memory" Version="4.5.0" />
+    <PackageReference Include="System.Memory" Version="4.6.3" />
     <PackageReference Include="System.Buffers" Version="4.6.1" />
   </ItemGroup>