test: fix running tests as non-root system user

[bdrung]

sbuild with the unshare backend will run as system user (but not root). This causes these two tests to fail:

=================================== FAILURES ===================================
_______________ TestApportCheckreports.test_has_no_system_report _______________

self = <tests.integration.test_apport_checkreports.TestApportCheckreports testMethod=test_has_no_system_report>

    def test_has_no_system_report(self) -> None:
        self._write_report("_bin_sleep.1000.crash")
> self._call(args=["--system"], expected_returncode=1)

tests/integration/test_apport_checkreports.py:68:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
tests/integration/test_apport_checkreports.py:53: in _call
    self.assertEqual(process.returncode, expected_returncode)
E AssertionError: 0 != 1
__________________________ T.test_get_system_reports ___________________________

self = <tests.integration.test_fileutils.T testMethod=test_get_system_reports>

    def test_get_system_reports(self) -> None:
        """get_all_system_reports() and get_new_system_reports()"""
        self.assertEqual(apport.fileutils.get_all_reports(), [])
        self.assertEqual(apport.fileutils.get_all_system_reports(), [])
        if os.getuid() == 0:
            tr = self._create_reports(True)
            self.assertEqual(set(apport.fileutils.get_all_system_reports()), set(tr))
            self.assertEqual(set(apport.fileutils.get_new_system_reports()), set(tr))

            # now mark them as seen and check again
            for r in tr:
                apport.fileutils.mark_report_seen(r)

            self.assertEqual(set(apport.fileutils.get_all_system_reports()), set(tr))
            self.assertEqual(set(apport.fileutils.get_new_system_reports()), set([]))
        else:
            tr = [r for r in self._create_reports(True) if "inaccessible" not in r]
> self.assertEqual(set(apport.fileutils.get_all_system_reports()), set([]))
E AssertionError: Items in the first set but not the second:
E '/tmp/tmp0l5zfk3h/rep2.crash'
E '/tmp/tmp0l5zfk3h/inaccessible.crash'
E '/tmp/tmp0l5zfk3h/rep1.crash'

tests/integration/test_fileutils.py:236: AssertionError
=============================== warnings summary ===============================

Skip test_has_no_system_report in this case, because the test would require to call os.chown(path, 1000, -1) which will fail with an permission error.

Bug: https://launchpad.net/bugs/2153134

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.38%. Comparing base (07b90b3) to head (3ba9d20).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #626   +/-   ##
=======================================
  Coverage   84.37%   84.38%           
=======================================
  Files         106      106           
  Lines       21035    21039    +4     
  Branches     3220     3221    +1     
=======================================
+ Hits        17749    17753    +4     
+ Misses       2803     2802    -1     
- Partials      483      484    +1     

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