A silent failure occurs if a file path listed in `filePushOrder` does not exist

> (Note: Non-breaking issues are likely not to be prioritized. Please consider a PR in addition to your issue)

## Expected Behavior

If a file path listed in `filePushOrder` does not exist, I would expect `clasp push` to fail with a clear error message.

## Actual Behavior

It just skips the missing file and continues as if nothing went wrong.

## Steps to Reproduce the Problem

1. Add a path to a non-existing file to `filePushOrder`
1. Run `clasp push`
1. Observe that the output to stdout and stderr includes no error message about the non-existing file path
1. Run `echo $?`
1. Observe that the exit code of `clasp push` is `0` but should have been non-zero.

## Specifications

- Node version (`node -v`): `v20.8.1`
- Version (`clasp -v`): `2.4.2`
- OS (Mac/Linux/Windows): macOS 13.6 22G120