dbtables.py: use close rather than unlink for NamedTemporaryFile clean up

3 jobs for tmp_unlink in 3 minutes and 44 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #844097
build-python27

00:02:19

passed #844098
build-python37

00:02:17

 
  Docs
passed #844099
docs

00:01:25