fix: incorrect stdout for mise shell function in xonsh

[yggdr]

The old implementation had issues with piping the result since stdout/stderr was not acutally captured in the shell but directly printed to the terminal. The fix here unfortunately effectivly turns off colors in mise, as mise seems to not honor CLICOLOR_FORCE et. al. environment variables as per #1836

[jdx]

I think it'd be better if we just found out why CLICOLOR_FORCE isn't working and fixed that directly

[yggdr]

The coloring problem is only a side-effect of this fix, so it should imho have no bearing on whether this fix should be accepted or not. The fix addresses stdio within the xonsh shell which I handled incorrectly, thereby breaking pipe-ability. You can read about that here: https://github.com/xonsh/xonsh/discussions/5316

[booniepepper]

I'd like to be able to fix the xonsh piping issue without regressing on color output.

[yggdr]

I'd rather have a functionally working shell incl. pipeability than colours, nice though they may be. That the colours work at all in xonsh with the current code is a mere accident and side effect of my buggy original implementation.