Fix file state=touch not returning diff information

Fixes #41755

changelogs/fragments/file_touch_diff.yaml

@@ -0,0 +1,4 @@
+---
+bugfixes:
+- file module - The touch subcommand had its diff output broken during the
+  2.6.x development cycle.  This is now fixed (https://github.com/ansible/ansible/issues/41755)

lib/ansible/modules/files/file.py

@@ -370,7 +370,7 @@ def execute_touch(path, follow):
             raise
 
     # Unfortunately, touch always changes the file because it updates file's timestamp
-    return {'dest': path, 'changed': True}
+    return {'dest': path, 'changed': True, 'diff': diff}
 
 
 def ensure_file_attributes(path, follow):