When launching Doom via 'doom run', the child process inherits
bin/doom's environment. This change restricts this sub-environment to
the intended target: straight and its use of git.
Fix: #6320
Reduces the amount of "noise" included in bin/doom's output.
Also fixes an issue where warnings during autoloads generation would
sneak into Doom's autoloads file, producing weird void-variable errors,
like
(void-variable . rainbow-delimiters:)
(void-variable . diredfl:)
(void-variable . company:)
