Version 2.6.9 of the Azure-Amqp package cannot be built using .Net Restore.

[LarryOsterman]

Repro steps:

git clone https://github.com/Azure/azure-amqp.git --branch v2.6.9
cd azure-amqp/test/TestAmqpBroker
dotnet publish --self-contained --frmework net6.0

Expected results:

Code builds without error.

Actual results:

C:\Program Files\dotnet\sdk\9.0.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.TargetFrameworkInference.targets(187,5): warning NETSDK1215: Targeting .NET Standard prior to 2.0 is no longer recommended. See https://aka.ms/dotnet/dotnet-standard-guidance for more details.
C:\Program Files\dotnet\sdk\9.0.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.EolTargetFrameworks.targets(32,5): warning NETSDK1138: The target framework 'net5' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.
<redacted>\source\repos\test\azure-amqp\Microsoft.Azure.Amqp\Microsoft.Azure.Amqp.csproj : error NU1903: Warning As Error: Package 'System.Net.Security' 4.0.0 has a known high severity vulnerability, https://github.com/advisories/GHSA-6xh7-4v2w-36q6
<redacted>\source\repos\test\azure-amqp\Microsoft.Azure.Amqp\Microsoft.Azure.Amqp.csproj : error NU1902: Warning As Error: Package 'System.Net.Security' 4.0.0 has a known moderate severity vulnerability, https://github.com/advisories/GHSA-ch6p-4jcm-h8vh
<redacted>\source\repos\test\azure-amqp\Microsoft.Azure.Amqp\Microsoft.Azure.Amqp.csproj : error NU1902: Warning As Error: Package 'System.Net.Security' 4.0.0 has a known moderate severity vulnerability, https://github.com/advisories/GHSA-j8f4-2w4p-mhjc
<redacted>\source\repos\test\azure-amqp\Microsoft.Azure.Amqp\Microsoft.Azure.Amqp.csproj : error NU1903: Warning As Error: Package 'System.Net.Security' 4.0.0 has a known high severity vulnerability, https://github.com/advisories/GHSA-qhqf-ghgh-x2m4