resetenv() always crashes #2068

Any use of resetenv() in the commands() function results in a traceback that ends with

  File "/laika/dist/third_party/linux_rocky9_x86_64/rez/v3.3.0/lib/python3.11/site-packages/rez/shells.py", line 137, in get_output
    script = '\n'.join(self._lines) + '\n'
             ^^^^^^^^^^^^^^^^^^^^^^
TypeError: sequence item 76: expected str instance, NoneType found

This is because resetenv() is set to the return value of setenv() but setenv() doesn't return anything. And even if it did, resetenv() wouldn't do what rezconfig.py implies that it would.

Environment

• OS rocky9.4
• Rez version 3.3.0
• Rez python version 3.11.12

To Reproduce

def commands():
    setenv("FOO", "value")
    resetenv("FOO", "new_value")

then build this package and do rez env <package_name>

Expected behavior
The variable 'FOO' would be reset to "new_value"

Actual behavior
Traceback as described above

Related Issues/PRs
I couldn't find any issues related to this