tests/test-username-newline.t

tests: fix deprecation warning about regex flags not at beginning of expr

This may only show up when running the tests under python3.6+. Currently the
only test that does this is test-patchbomb-tls.t, and it only uses (?i), so
that's all that's handled at the moment.

Differential Revision: https://phab.mercurial-scm.org/D7552

  $ hg init
  $ touch a

  $ unset HGUSER
  $ echo "[ui]" >> .hg/hgrc
  $ echo "username= foo" >> .hg/hgrc
  $ echo "          bar1" >> .hg/hgrc

  $ hg ci -Am m
  adding a
  abort: username 'foo\nbar1' contains a newline
  
  [255]
  $ rm .hg/hgrc

  $ HGUSER=`(echo foo; echo bar2)` hg ci -Am m
  adding a
  abort: username 'foo\nbar2' contains a newline
  
  [255]
  $ hg ci -Am m -u "`(echo foo; echo bar3)`"
  adding a
  transaction abort!
  rollback completed
  abort: username 'foo\nbar3' contains a newline!
  [255]