CSHARP-3430: Updated System.Buffers from 4.4.0 to 4.5.1 as required by DnsClient.NET 1.4.0.

Author: JamesKovacs

src/MongoDB.Driver.Core/MongoDB.Driver.Core.csproj

@@ -128,7 +128,7 @@
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.6.2" PrivateAssets="All" />
     <PackageReference Include="MongoDB.Libmongocrypt" Version="1.2.0" />
     <PackageReference Include="SharpCompress" Version="0.23.0" />
-    <PackageReference Include="System.Buffers" Version="4.4.0" />
+    <PackageReference Include="System.Buffers" Version="4.5.1" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net452'">

tests/MongoDB.Driver.Core.Tests/MongoDB.Driver.Core.Tests.csproj

@@ -55,7 +55,6 @@
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.6.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0" />
     <PackageReference Include="Moq" Version="4.9.0" />
-    <PackageReference Include="System.Buffers" Version="4.4.0" />
     <PackageReference Include="xunit" Version="2.4.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
   </ItemGroup>