test_runner: fix `duration_ms` to be milliseconds
result of running node -e "require('node:test').test((t, done)=>setTimeout(() => done(), 500))"
before:
TAP version 13
# Subtest: <anonymous>
ok 1 - <anonymous>
---
duration_ms: 0.501664977
...
1..1
# tests 1
# pass 1
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 0.562913893
after:
TAP version 13
# Subtest: <anonymous>
ok 1 - <anonymous>
---
duration_ms: 501.590752
...
1..1
# tests 1
# pass 1
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 530.935436
not sure whether this was intended or not