lang/janet: update to 1.42.1

[bsd.hsw_gmail.com]

Summary

Also add short patch from https://github.com/janet-lang/janet/pull/1891
to avoid crash on (os/mkdir "/")
os/mkdir will normally return false on an existing directory except for "/"

Signed-off-by: Christopher Hall <[e-mail]>

Test Plan

poudriere test/build on 15.1 AMD64(hardware) and AARCH64(qemu)
only ran on AMD64

[dave_freedave.net]

The patch-src_core_os.c will only be needed until next release, as it was merged upstream.

[dave_freedave.net]

not sure how I missed but title is "lag/janet" instead of "lang/janet", not sure if that if holding up merge or me aprroving it as a non-comitter (if so I apologize!)