Bump NSubstitute

Bumps the dotnet group in /docs/azure/sdk/snippets/unit-testing with 1 update: [NSubstitute](https://github.com/nsubstitute/NSubstitute).


Updates `NSubstitute` from 5.1.0 to 5.3.0
- [Release notes](https://github.com/nsubstitute/NSubstitute/releases)
- [Changelog](https://github.com/nsubstitute/NSubstitute/blob/main/CHANGELOG.md)
- [Commits](nsubstitute/NSubstitute@v5.1.0...v5.3.0)

---
updated-dependencies:
- dependency-name: NSubstitute
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dotnet
...

Signed-off-by: dependabot[bot] <[email protected]>

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

@@ -14,7 +14,7 @@
     <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.7.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="Moq" Version="[4.20.72]" /> <!-- Context: https://github.com/Azure/azure-sdk-for-net/issues/38111 -->
-    <PackageReference Include="NSubstitute" Version="5.1.0" />
+    <PackageReference Include="NSubstitute" Version="5.3.0" />
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>