Reapply update to dotnet-coverage 18.9.0 (536)

Author: AArnott

.config/dotnet-tools.json

@@ -10,7 +10,7 @@
       "rollForward": false
     },
     "dotnet-coverage": {
-      "version": "18.8.0",
+      "version": "18.9.0",
       "commands": [
         "dotnet-coverage"
       ],