tests: check the message a doctest traceback shows

IGNORE_EXCEPTION_DETAIL had doctest ignore everything past the colon, so the
two tracebacks of the tutorial asserted the exception type and nothing else: a
block claiming an entirely different message passed. Both already match to the
character. ELLIPSIS stays, for a message too long or too unstable to spell out.

Author: azmeuk

pyproject.toml

@@ -110,7 +110,7 @@ docstring-code-format = true
 
 [tool.pytest.ini_options]
 addopts = "--doctest-modules --doctest-glob='*.rst'"
-doctest_optionflags= "ALLOW_UNICODE IGNORE_EXCEPTION_DETAIL ELLIPSIS"
+doctest_optionflags= "ALLOW_UNICODE ELLIPSIS"
 
 [tool.mypy]
 plugins = [