Bump the dotnet group with 2 updates (#54035)

Bumps Azure.Core from 1.56.0 to 1.57.0
Bumps Microsoft.NET.Test.Sdk from 18.5.1 to 18.6.0

---
updated-dependencies:
- dependency-name: Azure.Core
  dependency-version: 1.57.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dotnet
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dotnet
...

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Author: dependabot[bot]

docs/azure/sdk/snippets/unit-testing/UnitTestingSampleApp.csproj

@@ -10,9 +10,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Azure.Core" Version="1.56.0" />
+    <PackageReference Include="Azure.Core" Version="1.57.0" />
     <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.11.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
     <PackageReference Include="Moq" Version="[4.20.72]" /> <!-- Context: https://github.com/Azure/azure-sdk-for-net/issues/38111 -->
     <PackageReference Include="NSubstitute" Version="5.3.0" />
     <PackageReference Include="xunit" Version="2.9.3" />