[docs] Update running_mypy.rst - fix typo (#14212)

Fix typo - remove an unneeded period


https://mypy.readthedocs.io/en/stable/running_mypy.html#ignore-missing-imports

![image](https://user-images.githubusercontent.com/36337649/204286512-34a07d28-5417-4857-87a6-f910b33fb81f.png)

docs/source/running_mypy.rst

@@ -250,7 +250,7 @@ If you are getting this error, try:
 1.  Upgrading the version of the library you're using, in case a newer version
     has started to include type hints.
 
-2.  Searching to see if there is a :ref:`PEP 561 compliant stub package <installed-packages>`.
+2.  Searching to see if there is a :ref:`PEP 561 compliant stub package <installed-packages>`
     corresponding to your third party library. Stub packages let you install
     type hints independently from the library itself.