Google-Cloud-Storage-Upload | Used for dump backup | Continuous Backup library

According to the documentation:

The only writeable part of the filesystem is the /tmp directory, which you can use to store temporary files in a function instance. This is a local disk mount point known as a "tmpfs" volume in which data written to the volume is stored in memory. Note that it will consume memory resources provisioned for the function.

The rest of the file system is read-only and accessible to the function.

You should use os.tmpdir() to get the best writable directory for the current runtime.