python: fix and extend pyclean (#7762)

Deleting `.mypy_cache` did not work, because the directories were not
empty.  They contain JSON files instead of compiled byte-code.

This extends the cleanup by also getting rid of `.pytest_cache`
directories.

plugins/python/python.plugin.zsh

 # Find python file
 alias pyfind='find . -name "*.py"'
 
-# Remove python compiled byte-code and mypy cache in either current directory or in a
-# list of specified directories
+# Remove python compiled byte-code and mypy/pytest cache in either the current
+# directory or in a list of specified directories (including sub directories).
 function pyclean() {
     ZSH_PYCLEAN_PLACES=${*:-'.'}
     find ${ZSH_PYCLEAN_PLACES} -type f -name "*.py[co]" -delete
     find ${ZSH_PYCLEAN_PLACES} -type d -name "__pycache__" -delete
-    find ${ZSH_PYCLEAN_PLACES} -type d -name ".mypy_cache" -delete
+    find ${ZSH_PYCLEAN_PLACES} -depth -type d -name ".mypy_cache" -exec rm -r "{}" +
+    find ${ZSH_PYCLEAN_PLACES} -depth -type d -name ".pytest_cache" -exec rm -r "{}" +
 }
 
 # Grep among .py files