fix typo (#8069)

Author: jugmac00

src/_pytest/_argcomplete.py

@@ -26,7 +26,7 @@
 uses a python program to determine startup script generated by pip.
 You can speed up completion somewhat by changing this script to include
   # PYTHON_ARGCOMPLETE_OK
-so the the python-argcomplete-check-easy-install-script does not
+so the python-argcomplete-check-easy-install-script does not
 need to be called to find the entry point of the code and see if that is
 marked  with PYTHON_ARGCOMPLETE_OK.