bpo-41775: Make 'IDLE Shell' the shell title  (#22399)

'Python Shell' may have contributed to some beginners confusing 'IDLE' with ' Python'.
diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index 66ae0f7..b69916d 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -833,7 +833,7 @@
 
 class PyShell(OutputWindow):
 
-    shell_title = "Python " + python_version() + " Shell"
+    shell_title = "IDLE Shell " + python_version()
 
     # Override classes
     ColorDelegator = ModifiedColorDelegator