Ensure standard locale in run_command (group5-batch5) (#11776)
* Fix locale env vars in run_command() calls for group5 batch5 modules
Set LANGUAGE=C and LC_ALL=C via run_command_environ_update to ensure
locale-independent output parsing in pnpm, sysrc, timezone, xattr,
and yarn.
* Add changelog fragment for PR #11776
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(cherry picked from commit e45e6cbb5d)
Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
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