fix(ci): restore cwd after CUSTOM_SCRIPTS (iOS cd ios breaks later steps)

The iOS CUSTOM_SCRIPTS variable contains 'cd ios && pod install' which
changes the working directory. Subsequent steps (android SDK check,
metro cleanup, mkdir, emb) then run from the wrong directory.

Fix: save APP_DIR before CUSTOM_SCRIPTS, restore it after.
1 job for main in 1 minute and 44 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #127737
studio-2023 triggered
ci-build

00:01:44

 
Name Stage Failure
failed
ci-build Build
  output: [ null, null, null ],
pid: 85736,
stdout: null,
stderr: null
}

Node.js v18.18.2
Cleaning up project directory and file based variables
ERROR: Job failed: exit status 1