C#: Update global.json for cshtml_standalone_flowsteps.

Author: michaelnebel

csharp/ql/integration-tests/all-platforms/cshtml_standalone_flowsteps/global.json

@@ -1,5 +1,5 @@
 {
     "sdk": {
-        "version": "8.0.300"
+        "version": "9.0.100"
     }
 }