fix make error on ci.rst and tests.rst

[Prodesire]

when make html, we will occur errors below:

/**/python-guide/docs/writing/tests.rst:214: WARNING: Error in "code-block" directive:
1 argument(s) required, 0 supplied.

.. code-block::

Falsifying example: test_mean(
xs=[1.7976321109618856e+308, 6.102390043022755e+303]
)

/**/python-guide/docs/scenarios/ci.rst:7: WARNING: unknown document: writing/tests

[kennethreitz]

excellence