Update cron.py (#46055)

<!--- Your description here -->
The documentation states the use of the "value" attribute for environment variables while this should also be the "job" attribute.
+label: docsite_pr

lib/ansible/modules/system/cron.py

@@ -157,13 +157,13 @@ EXAMPLES = '''
   cron:
     name: PATH
     env: yes
-    value: /opt/bin
+    job: /opt/bin
 
 - name: Creates an entry like "APP_HOME=/srv/app" and insert it after PATH declaration
   cron:
     name: APP_HOME
     env: yes
-    value: /srv/app
+    job: /srv/app
     insertafter: PATH
 
 - name: Creates a cron file under /etc/cron.d