run-tests-on-os.yml: Added task to install .NET Core SDK 2.1
run-tests-on-os.yml: Added task to install .NET Core SDK 2.1

NightOwl888/lucenenet,apache/lucenenet,sisve/lucenenet,jeme/lucenenet,sisve/lucenenet,apache/lucenenet,jeme/lucenenet,jeme/lucenenet,jeme/lucenenet,NightOwl888/lucenenet,NightOwl888/lucenenet,apache/lucenenet,apache/lucenenet,NightOwl888/lucenenet