updated runs-on to reffer to matrix.os

Author: Petr Sramek

.github/workflows/dotnet.yml

@@ -37,7 +37,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-    runs-on: $
+    runs-on: ${{ matrix.os }}
 
     concurrency:
       group: becnhmark-group