repl: Don't wait on incomplete parses from imported file (backport #13334)

[mergify]

Motivation

The repl should only catch "unexpected end of file" parse errors from the top-level expression, not from imported files.

Fixes #13332.

Context

---

Add 👍 to pull requests you find important.

The Nix maintainer team uses a GitHub project board to schedule and track reviews.

---

This is an automatic backport of pull request #13334 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of d8b067b has failed:

On branch mergify/bp/2.28-maintenance/pr-13334
Your branch is up to date with 'origin/2.28-maintenance'.

You are currently cherry-picking commit d8b067b54.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   tests/functional/repl.sh

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/libcmd/repl.cc

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally