AppImage: give execute permission on scripts to Group and World

[shoogle]

Resolves: no issue in tracker

Old permissions: rwxr--r-- (Owner can execute)
New permissions: rwxr-xr-x (Owner, Group and World can execute)

Owner execute is not enough because the files are owned by root at runtime
(the AppImage is mounted this way by FUSE). Normally the permissions are
ignored, but they matter when trying to run the AppImage inside a sandbox
with an application like Firejail.

See AppImage/appimage.github.io#1943

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• [N/A] I created the test (mtest, vtest, script test) to verify the changes I made