Task: Make cabal-testsuite Unicode-tolerant

When trying to write a test-case for #5804 (e.g. a package having non-ascii utf8 encoded characters in its package name) I ran into problems as the testsuite would complain about unicode output on stdout

Start by locating the cabal-testsuite handling for stdout and the test case related to issue #5804. Reproduce the failure with non-ASCII UTF-8 output, then verify that the testsuite accepts it without complaining about Unicode output.

Written by the indexing model from the issue text.