Add execute permission to /data/app-staging folder

Package verifiers (e.g, phonesky) needs to access the folders inside
/data/app-staging to be able to verify them. Without the execute
permission on app-staging folder, it cannot stat any of the sub-dirs
inside app-staging.

This also aligns with permission of /data/app folder.

Bug: 175163376
Test: manual
Test: installed a staged session and observed that Phonesky did not log
about not finding the apks in /data/app-staging folder

Change-Id: I9774ed800da9f15401d3cee653142a37bf54ef4a