Bump RestSharp from 108.0.1 to 112.0.0 in /src/Dropbox.Sign

Bumps [RestSharp](https://github.com/restsharp/RestSharp) from 108.0.1 to 112.0.0.
- [Release notes](https://github.com/restsharp/RestSharp/releases)
- [Commits](restsharp/RestSharp@108.0.1...112.0.0)

---
updated-dependencies:
- dependency-name: RestSharp
  dependency-type: direct:production
...

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

src/Dropbox.Sign/Dropbox.Sign.csproj

@@ -22,7 +22,7 @@
   <ItemGroup>
     <PackageReference Include="JsonSubTypes" Version="1.9.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
-    <PackageReference Include="RestSharp" Version="108.0.1" />
+    <PackageReference Include="RestSharp" Version="112.0.0" />
     <PackageReference Include="Polly" Version="7.2.3" />
     <PackageReference Include="System.ComponentModel.Annotations" Version="5.0.0" />
   </ItemGroup>