do not line break reference

Doc/library/unittest.rst

@@ -1755,13 +1755,13 @@ Loading and running tests
 
    By default this runner shows :exc:`DeprecationWarning`,
    :exc:`PendingDeprecationWarning`, :exc:`ResourceWarning` and
-   :exc:`ImportWarning` even if they are :ref:`ignored by default <warning-
-   ignored>`. Deprecation warnings caused by :ref:`deprecated unittest methods
-   <deprecated-aliases>` are also special-cased and, when the warning filters
-   are ``'default'`` or ``'always'``, they will appear only once per-module, in
-   order to avoid too many warning messages.  This behavior can be overridden
-   using the :option:`-Wd` or :option:`-Wa` options and leaving *warnings* to
-   ``None``.
+   :exc:`ImportWarning` even if they are :ref:`ignored by default
+   <warning-ignored>`. Deprecation warnings caused by :ref:`deprecated unittest
+   methods <deprecated-aliases>` are also special-cased and, when the warning
+   filters are ``'default'`` or ``'always'``, they will appear only once
+   per-module, in order to avoid too many warning messages.  This behavior can
+   be overridden using the :option:`-Wd` or :option:`-Wa` options and leaving
+   *warnings* to ``None``.
 
    .. versionchanged:: 3.2
       Added the ``warnings`` argument.