cmd/go: make module .zip files group/world readable
cmd/go: make module .zip files group/world readable

os.CreateTemp in downloadZip leaves downloaded .zip files readable only
by the owner. Make them group/world readable.

Fixes #52765

Change-Id: Iace13e4ad813201a533a1a5fc0c6d9b2e5349a42
Reviewed-on: https://go-review.googlesource.com/c/go/+/404854
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

nawawi/go,golang/go,nawawi/go,golang/go,golang/go,golang/go,golang/go,nawawi/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go