Doc: Update Preferences > Environment > System screenshot

Task-number: QTCREATORBUG-29392
Change-Id: Ic8ccedfbcb3f6aeb139f969bde1c439c78720941
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

doc/qtcreator/src/howto/creator-only/creator-how-tos.qdoc

@@ -412,7 +412,7 @@
 
     \list 1
         \li Select \preferences > \uicontrol Environment > \uicontrol System.
-            \image qtcreator-options-environment-system.png {System preferences}
+            \image qtcreator-preferences-environment-system.webp {System preferences}
         \li In \uicontrol {Maximum number of entries in "Recent Files"}, set
             the number of files to show.
     \endlist

doc/qtcreator/src/projects/creator-only/creator-projects-settings-environment.qdoc

@@ -23,7 +23,7 @@
     \uicontrol Environment > \uicontrol System, and then select
     \uicontrol Change in the \uicontrol Environment field.
 
-    \image qtcreator-options-environment-system.png "Environment preferences System tab"
+    \image qtcreator-preferences-environment-system.webp "Environment preferences System tab"
 
     In addition, you can specify custom environment variables in the
     \uicontrol {Project Settings} > \uicontrol Environment settings.

doc/qtcreator/src/user-interface/creator-open-documents-view.qdoc

@@ -38,7 +38,7 @@
     To set preferences for opening files and handling open files, select
     \preferences > \uicontrol Environment > \uicontrol System:
 
-    \image qtcreator-options-environment-system.png {System tab in Environment preferences}
+    \image qtcreator-preferences-environment-system.webp {System tab in Environment preferences}
 
     \list
         \li In the \uicontrol {When files are externally modified} field,