changelog: Fix tox check environment

Change the duplicate links to anonymous references.

Author: fetzerch

CHANGELOG.rst

@@ -44,10 +44,10 @@ Changelog
 -------------------
 
 * Changed the `toml` requirement to be always be directly required (instead of being required through a coverage extra).
-  This fixes issues with pip-compile (`pip-tools#1300 <https://github.com/jazzband/pip-tools/issues/1300>`_).
-  Contributed by Sorin Sbarnea in `#472 <https://github.com/pytest-dev/pytest-cov/pull/472>`_.
+  This fixes issues with pip-compile (`pip-tools#1300 <https://github.com/jazzband/pip-tools/issues/1300>`__).
+  Contributed by Sorin Sbarnea in `#472 <https://github.com/pytest-dev/pytest-cov/pull/472>`__.
 * Documented ``show_contexts``.
-  Contributed by Brian Rutledge in `#473 <https://github.com/pytest-dev/pytest-cov/pull/473>`_.
+  Contributed by Brian Rutledge in `#473 <https://github.com/pytest-dev/pytest-cov/pull/473>`__.
 
 
 2.12.1 (2021-06-01)
@@ -200,7 +200,7 @@ Changelog
   `#271 <https://github.com/pytest-dev/pytest-cov/pull/271>`_ and
   `#269 <https://github.com/pytest-dev/pytest-cov/pull/269>`_.
 * Improved documentation regarding subprocess and multiprocessing.
-  Contributed in `#265 <https://github.com/pytest-dev/pytest-cov/pull/265>`_.
+  Contributed in `#265 <https://github.com/pytest-dev/pytest-cov/pull/265>`__.
 * Improved ``pytest_cov.embed.cleanup_on_sigterm`` to be reentrant (signal deliveries while signal handling is
   running won't break stuff).
 * Added ``pytest_cov.embed.cleanup_on_signal`` for customized cleanup.