pkg/archive: adjust chmod bits on windows

This change modifies the chmod bits of build context archives built on
windows to preserve the execute bit and remove the r/w bits from
grp/others.

Also adjusted integ-cli tests to verify permissions based on the platform
the tests are running.

Fixes #11047.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>