Fix TwistedSystem (plugin for pydoctor)

[twisted-trac]

	@mthuurne reported
Trac ID	trac#10044
Type	defect
Created	2020-10-28 14:13:44Z

This is a subitem split off from #10035.

It turns out the unit tests for TwistedSystem were skipped by accident, so they haven't been run in years. And of course, when re-enabled, they fail.

It's not only the tests that fail though: showing deprecations in the generated API docs is broken too.

Searchable metadata

trac-id__10044 10044
type__defect defect
reporter__mthuurne mthuurne
priority__normal normal
milestone__None None
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__pydoctor pydoctor
keywords__None None
time__1603894424783916 1603894424783916
changetime__1604424557140229 1604424557140229
version__None None
owner__Adi_Roiban__adiroiban_____ Adi Roiban <adiroiban@...>

[twisted-trac]

	@adiroiban set owner to @adiroiban @adiroiban set status to closed

In changeset ff991d7

#!CommitTicketReference repository="" revision="ff991d784a5d6a95f540786965a406404dab7469"
Merge pull request #1473 from twisted/fix-twistedsystem-for-pydoctor

Author: mthuurne, adiroiban
Reviewer:  graingert, adiroiban
Fixes: ticket:10044

Re-enable release tests. Fix the tests for py3 update.