fix(pyenv)!: do not load if a virtualenv is present

BREAKING CHANGE: `pyenv` will not be loaded at startup anymore if a
virtual env if found to avoid overwriting the expected python version.

Closes #12589

plugins/pyenv/README.md

@@ -2,7 +2,7 @@
 
 This plugin looks for [pyenv](https://github.com/pyenv/pyenv), a Simple Python version
 management system, and loads it if it's found. It also loads pyenv-virtualenv, a pyenv
-plugin to manage virtualenv, if it's found.
+plugin to manage virtualenv, if it's found. If a venv is found pyenv won't load.
 
 To use it, add `pyenv` to the plugins array in your zshrc file:
 

plugins/pyenv/pyenv.plugin.zsh

@@ -1,3 +1,7 @@
+# if there is a virtualenv already loaded pyenv should not be loaded
+# see https://github.com/ohmyzsh/ohmyzsh/issues/12589
+[[ -n ${VIRTUAL_ENV:-} ]] && return
+
 pyenv_config_warning() {
   [[ "$ZSH_PYENV_QUIET" != true ]] || return 0