2.5.0 + master: sphinx warnings `reference target not found`

[kloczek]

On building my packages I'm using sphinx-build command with -n switch which shows warmings about missing references. These are not critical issues.
Here is the output with warnings:

+ /usr/bin/sphinx-build -n -T -b man doc build/sphinx/man
Running Sphinx v4.5.0
making output directory... done
loading intersphinx inventory from https://docs.python.org/2/objects.inv...
loading intersphinx inventory from https://docs.python.org/3/objects.inv...
loading intersphinx inventory from https://twistedmatrix.com/documents/current/api/objects.inv...
building [mo]: targets for 0 po files that are out of date
building [man]: all manpages
updating environment: [new config] 8 added, 0 changed, 0 removed
reading sources... [100%] twisted-support
/usr/lib/python3.8/site-packages/testtools/matchers/__init__.py:docstring of testtools.matchers._warnings.WarningMessage:1: WARNING: Inline interpreted text or phrase reference start-string without end-string.
/usr/lib/python3.8/site-packages/testtools/matchers/__init__.py:docstring of testtools.matchers._warnings.WarningMessage:14: WARNING: Field list ends without a blank line; unexpected unindent.
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
writing... python-testtools.3 { overview for-test-authors for-framework-folk twisted-support hacking news api } /usr/lib/python3.8/site-packages/testtools/twistedsupport/_matchers.py:docstring of testtools.twistedsupport._matchers.succeeded:13: WARNING: py:meth reference target not found: twisted.trial.unittest.SynchronousTestCase.successResultOf
/usr/lib/python3.8/site-packages/testtools/twistedsupport/_matchers.py:docstring of testtools.twistedsupport._matchers.failed:15: WARNING: py:meth reference target not found: twisted.trial.unittest.SynchronousTestCase.failureResultOf
/usr/lib/python3.8/site-packages/testtools/testcase.py:docstring of testtools.testcase.TestCase.assertThat:: WARNING: py:exc reference target not found: MismatchError
<unknown>:1: WARNING: py:class reference target not found: unittest.case.SkipTest
/usr/lib/python3.8/site-packages/testtools/assertions.py:docstring of testtools.assertions.assert_that:: WARNING: py:exc reference target not found: MismatchError
/usr/lib/python3.8/site-packages/testtools/twistedsupport/__init__.py:docstring of testtools.twistedsupport._runtest.assert_fails_with:: WARNING: py:class reference target not found: Deferred
/usr/lib/python3.8/site-packages/testtools/twistedsupport/__init__.py:docstring of testtools.twistedsupport._matchers.failed:15: WARNING: py:meth reference target not found: twisted.trial.unittest.SynchronousTestCase.failureResultOf
/usr/lib/python3.8/site-packages/testtools/twistedsupport/__init__.py:docstring of testtools.twistedsupport._matchers.succeeded:13: WARNING: py:meth reference target not found: twisted.trial.unittest.SynchronousTestCase.successResultOf
done
build succeeded, 10 warnings.

Above output is against current master.