Reproduce steps:

1. Emacs -Q

2. M-x eval-expression `(setenv "PATH" (concat "C:/env" path-separator (getenv "PATH")))`

3. M-x eshell

4. In the *eshell* window, type `echo $PATH`, but the path "C:/env" doesn't show in the result.

P.S. I have also tried `eshell-set-path` and `with-environment-variables`, but they cannot set PATH as well. For example,
(defun eshell2()
  (interactive)
  (eshell-set-path '("C:/env"))
  (call-interactively 'eshell))

(defun eshell3()
  (interactive)
  (with-environment-variables (("PATH" (concat "C:/env" path-separator (getenv "PATH"))))