Bump nuget/helpers/lib/dotnet-core from 218ef74 to ff55a93

Bumps [nuget/helpers/lib/dotnet-core](https://github.com/dotnet/core) from `218ef74` to `ff55a93`.
- [Release notes](https://github.com/dotnet/core/releases)
- [Commits](dotnet/core@218ef74...ff55a93)

---
updated-dependencies:
- dependency-name: nuget/helpers/lib/dotnet-core
  dependency-version: ff55a933e5caa3025615b66508824c2dbc7e8a42
  dependency-type: direct:production
...

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

Author: dependabot[bot]