bpo-31649: Make IDLE's _htest, _utest parameters keyword-only. (#3839)

diff --git a/Lib/idlelib/browser.py b/Lib/idlelib/browser.py
index 603d299..9b32315 100644
--- a/Lib/idlelib/browser.py
+++ b/Lib/idlelib/browser.py
@@ -61,7 +61,7 @@
     # This class is the base class for pathbrowser.PathBrowser.
     # Init and close are inherited, other methods are overriden.
 
-    def __init__(self, flist, name, path, _htest=False, _utest=False):
+    def __init__(self, flist, name, path, *, _htest=False, _utest=False):
         # XXX This API should change, if the file doesn't end in ".py"
         # XXX the code here is bogus!
         """Create a window for browsing a module's structure.