Include AWSSDK.SecurityToken in Lambda Test Tool runtime payload

The packaged Lambda Test Tool global tool does not ship
AWSSDK.SecurityToken.dll, so any code path that resolves credentials
via AssumeRoleAWSCredentials (profiles with role_arn, etc.) crashes
with FileNotFoundException when the SDK reflectively loads the
assembly to construct an STS client.

Add a direct PackageReference so the DLL ships in tools/<tfm>/any/.

Author: AlexDaines

Tools/LambdaTestTool-v2/src/Amazon.Lambda.TestTool/Amazon.Lambda.TestTool.csproj

@@ -25,6 +25,7 @@
     <PackageReference Include="Amazon.Lambda.SQSEvents" Version="2.2.1" />
     <PackageReference Include="AWSSDK.Extensions.NETCore.Setup" Version="4.0.3.22" />
     <PackageReference Include="AWSSDK.Lambda" Version="4.0.13.1" />
+    <PackageReference Include="AWSSDK.SecurityToken" Version="4.0.6.3" />
     <PackageReference Include="AWSSDK.SQS" Version="4.0.2.14" />
     <PackageReference Include="AWSSDK.SSO" Version="4.0.2.13" />
     <PackageReference Include="AWSSDK.SSOOIDC" Version="4.0.3.14" />