Executable bit reset between build and invoke

I have a function where the build script clones a Git repo which has an executable in it. If I chmod +x the file in the build script I can run it like ./foo in the build script and it runs fine there. However, when I invoke my function which has a bash script that runs ./foo I get “Permission denied” unless I explicitly run chmod +x on the executable every time the function is invoked.

My runtime is Python and my code just calls the bash script like so: os.system('bash ./run.sh').

I’m at a loss. Any ideas? I don’t want to have to chmod +x every time the function is invoked.