Bump Microsoft.Extensions.Configuration.EnvironmentVariables

Bumps [Microsoft.Extensions.Configuration.EnvironmentVariables](https://github.com/aspnet/Extensions) from 3.1.7 to 3.1.8.
- [Release notes](https://github.com/aspnet/Extensions/releases)
- [Commits](dotnet/extensions@v3.1.7...v3.1.8)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

src/SignClient/SignClient.csproj

@@ -13,7 +13,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.CommandLineUtils" Version="1.1.1" />
-    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="3.1.7" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="3.1.8" />
     <PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="3.1.7" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="3.1.7" />
     <PackageReference Include="Microsoft.Identity.Client" Version="4.18.0" />