tests/test-config-case.t

tests: don't hardcode errno==2 for ENOENT

Hurd seems to set ENOENT to 2 + 2**30, unlike everyone else.

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  $ hg init

  $ echo '[Section]' >> $HGRCPATH
  $ echo 'KeY = Case Sensitive' >> $HGRCPATH
  $ echo 'key = lower case' >> $HGRCPATH

  $ hg showconfig Section
  Section.KeY=Case Sensitive
  Section.key=lower case