test_runner: fix infinite loop when files are undefined in test runner

fix: #48823 (closed)

code:

import { run } from 'node:test'
import { tap } from 'node:test/reporters';

const stream = run({ files: undefined }).compose(tap)

stream.pipe(process.stdout);

running without --test flag

TAP version 13
# TAP version 13
# 1..0
# \# tests 0
# \# suites 0
# \# pass 0
# \# fail 0
# \# cancelled 0
# \# skipped 0
# \# todo 0
# \# duration_ms 4.814625
# Subtest: /Users/pulkitgupta/Desktop/node/index.mjs
ok 1 - /Users/pulkitgupta/Desktop/node/index.mjs
  ---
  duration_ms: 68.923583
  ...
1..1
# tests 1
# suites 0
# pass 1
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 76.718041

running with --test flag.

TAP version 13
1..0
# tests 0
# suites 0
# pass 0
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 5.461375
✔ index.mjs (81.525375ms)
ℹ tests 1
ℹ suites 0
ℹ pass 1
ℹ fail 0
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0
ℹ duration_ms 93.773375