feat(grep): exclude Python virtualenv from `grep` (#12685)

The convention to use `.venv` or `venv` directories for Python virtualenvs is widespread. 
This directory is huge and gives very little value when grepping in a source code directory.

Co-authored-by: Marc Cornellà <marc@mcornella.com>

lib/grep.zsh

@@ -10,7 +10,7 @@ else
     }
 
     # Ignore these folders (if the necessary grep flags are available)
-    EXC_FOLDERS="{.bzr,CVS,.git,.hg,.svn,.idea,.tox}"
+    EXC_FOLDERS="{.bzr,CVS,.git,.hg,.svn,.idea,.tox,.venv,venv}"
 
     # Check for --exclude-dir, otherwise check for --exclude. If --exclude
     # isn't available, --color won't be either (they were released at the same