Perform Gatekeeper scan and still use new temp directory for installs

[zorgiepoo]

This restores using a new temporary directory before swapping the app update (when the bundles are on the same volume). It turns out it is still a good idea to have this. This also seems to allow doing the gatekeeper scan without any issues on macOS Sonoma.

Misc Checklist

• My change requires a documentation update on Sparkle's website repository
• My change requires changes to generate_appcast, generate_keys, or sign_update

Only bug fixes to regressions or security fixes are being backported to the 1.x (master) branch now. If you believe your change is significant enough to backport, please also create a separate pull request against the master branch.

Testing

I tested and verified my change by using one or multiple of these methods:

• Sparkle Test App
• Unit Tests
• My own app
• Other (please specify)

Tested updating notarized app
Tested updating unsigned app
Tested updating app on different volume (USB drive)

macOS version tested: 14.0 Beta (23A5337a)