Incomplete Process Termination Process (#2205)

The Notepad process was not terminating after the command execution
Line Added: 
taskkill /im notepad.exe /t /f > NUL 2>&1
 
The /t option makes sure any child processes are closed as well, and the /f option forcefully terminates the process.
The > NUL redirects the stdout to the NUL device (the equivalent of /dev/null) and the 2 >&1 also redirects the stderr to stdout so that nothing is output to the console

atomics/T1546.007/T1546.007.yaml

@@ -27,7 +27,8 @@ atomic_tests:
   executor:
     command: |
       netsh.exe add helper #{helper_file}
+      taskkill /im notepad.exe /t /f > NUL 2>&1
     cleanup_command: |
       netsh.exe delete helper #{helper_file}
     name: command_prompt
-    elevation_required: true
+    elevation_required: true