Bump MessagePack from 2.5.171 to 2.5.187 in /src/bctklib (#467)

Bumps [MessagePack](https://github.com/MessagePack-CSharp/MessagePack-CSharp) from 2.5.171 to 2.5.187.
- [Release notes](https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases)
- [Changelog](https://github.com/MessagePack-CSharp/MessagePack-CSharp/blob/master/prepare_release.ps1)
- [Commits](MessagePack-CSharp/MessagePack-CSharp@v2.5.171...v2.5.187)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/bctklib/bctklib.csproj

@@ -14,7 +14,7 @@
         <InternalsVisibleTo Include="test.bctklib" />
     </ItemGroup>
     <ItemGroup>
-        <PackageReference Include="MessagePack" Version="2.5.171" />
+        <PackageReference Include="MessagePack" Version="2.5.187" />
         <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="all" />
         <PackageReference Include="Neo" Version="3.7.6" />
         <PackageReference Include="Nerdbank.Streams" Version="2.11.74" />