[release/v7.2.7] On Unix, only explicitly terminate the native process if not in background (#18280)

Co-authored-by: Steve Lee <slee@microsoft.com>

Author: TravisEz13

src/System.Management.Automation/engine/NativeCommandProcessor.cs

@@ -326,7 +326,7 @@ internal override void Prepare(IDictionary psDefaultParameterValues)
             catch (Exception)
             {
                 // Do cleanup in case of exception
-                CleanUp();
+                CleanUp(killBackgroundProcess: true);
                 throw;
             }
         }
@@ -348,7 +348,7 @@ internal override void ProcessRecord()
             catch (Exception)
             {
                 // Do cleanup in case of exception
-                CleanUp();
+                CleanUp(killBackgroundProcess: true);
                 throw;
             }
         }
@@ -782,7 +782,7 @@ internal override void Complete()
             finally
             {
                 // Do some cleanup
-                CleanUp();
+                CleanUp(killBackgroundProcess: false);
             }
 
             // An exception was thrown while attempting to run the program
@@ -1060,7 +1060,8 @@ internal void StopProcessing()
         /// <summary>
         /// Aggressively clean everything up...
         /// </summary>
-        private void CleanUp()
+        /// <param name="killBackgroundProcess">If set, also terminate background process.</param>
+        private void CleanUp(bool killBackgroundProcess)
         {
             // We need to call 'NotifyEndApplication' as appropriate during cleanup
             if (_hasNotifiedBeginApplication)
@@ -1070,23 +1071,23 @@ private void CleanUp()
 
             try
             {
-                if (_nativeProcess != null)
-                {
-                    // on Unix, we need to kill the process to ensure it terminates as Dispose() merely
-                    // closes the redirected streams and the processs does not exit on macOS.  However,
-                    // on Windows, a winexe like notepad should continue running so we don't want to kill it.
+                // on Unix, we need to kill the process (if not running in background) to ensure it terminates,
+                // as Dispose() merely closes the redirected streams and the process does not exit.
+                // However, on Windows, a winexe like notepad should continue running so we don't want to kill it.
 #if UNIX
+                if (killBackgroundProcess || !_isRunningInBackground)
+                {
                     try
                     {
-                        _nativeProcess.Kill();
+                        _nativeProcess?.Kill();
                     }
                     catch
                     {
-                        // Ignore all exception since it is cleanup.
+                        // Ignore all exceptions since it is cleanup.
                     }
-#endif
-                    _nativeProcess.Dispose();
                 }
+#endif
+                _nativeProcess.Dispose();
             }
             catch (Exception)
             {