Comment 4 for bug 1968415

I have this test failure now:
```
running=PYTHONPATH=`pwd`:$PYTHONPATH BRZ_PLUGIN_PATH=-site:-user ./brz selftest --subunit2
======================================================================
FAIL: breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail(GioTransport,GioLocalURLServer)
tags: worker-0
----------------------------------------------------------------------
log: {{{
107.096 creating repository in file:///tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail%28GioTransport%2CGioLocalURLServer%29/work/tree/.bzr/.
107.097 creating branch <breezy.bzr.branch.BzrBranchFormat7 object at 0x7fffd6983970> in file:///tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail%28GioTransport%2CGioLocalURLServer%29/work/tree/
107.101 trying to create missing lock '/tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail(GioTransport,GioLocalURLServer)/work/tree/.bzr/checkout/dirstate'
107.101 opening working tree '/tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail(GioTransport,GioLocalURLServer)/work/tree'
107.107 preparing to commit
    INFO Committing to: /tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail(GioTransport,GioLocalURLServer)/work/tree/
107.108 Selecting files for commit with filter None
    INFO added a
    INFO added subdir
    INFO Committed revision 1.
107.114 Committed revid b'commit-1' as revno 1.
    INFO Bundling 1 revision.
107.121 Put to: gio+file:///tmp/guix-build-breezy-3.2.2.drv-0/testbzr-7s_jteq5.tmp/breezy.bzr.tests.test_read_bundle.TestReadMergeableBundleFromURL.test_read_fail%28GioTransport%2CGioLocalURLServer%29/work/test_bundle
}}}

Traceback (most recent call last):
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/bzr/tests/test_read_bundle.py", line 98, in test_read_fail
    self.assertRaises(errors.NotABundle,
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/tests/__init__.py", line 1472, in assertRaises
    callableObj(*args, **kwargs)
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/bzr/tests/test_read_bundle.py", line 72, in read_mergeable_from_url
    return breezy.mergeable.read_mergeable_from_url(
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/mergeable.py", line 64, in read_mergeable_from_url
    mergeable, transport = read_mergeable_from_transport(transport, filename,
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/mergeable.py", line 82, in read_mergeable_from_transport
    bytef, transport = _mod_transport.do_catching_redirections(
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/transport/__init__.py", line 1613, in do_catching_redirections
    return action(transport)
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/mergeable.py", line 71, in get_bundle
    return BytesIO(transport.get_bytes(filename)), transport
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/transport/__init__.py", line 628, in get_bytes
    f = self.get(relpath)
  File "/tmp/guix-build-breezy-3.2.2.drv-0/breezy-3.2.2/breezy/transport/gio_transport.py", line 283, in get
    return BytesIO(buf)
TypeError: a bytes-like object is required, not '_ResultTuple'
======================================================================
FAIL: process-returncode
tags: worker-0
----------------------------------------------------------------------
returncode -11
Ran 5484 tests in 104.758s
FAILED (id=0, failures=3, skips=679)
```