Repair doc markup.

Author: nascheme

Doc/using/cmdline.rst

@@ -978,10 +978,10 @@ conflict.
 
 .. envvar:: PYTHON_GC_THRESHOLD
 
-   Set the `threshold0` value for the garbage collector.  This is the same
-   as calling `gc.set_threshold(n)` where `n` is value of the variable.  Using
-   an empty value or the value "default" will cause the default threshold to be
-   used.
+   Set the ``threshold0`` value for the garbage collector.  This is the same as
+   calling ``gc.set_threshold(n)`` where ``n`` is value of the variable. Using
+   an empty value or the value ``default`` will cause the default threshold to
+   be used.
 
    .. versionadded:: 3.13
 

Misc/NEWS.d/next/Core_and_Builtins/2024-09-28-20-01-40.gh-issue-124742.7kJx88.rst

@@ -1,4 +1,4 @@
-Add the `PYTHON_GC_THRESHOLD` environment variable.  This can be used to set
-the `threshold0` value for the garbage collector, similar to calling
-`gc.set_threshold()`.  If the value is empty or "default", the default
+Add the :envvar:`PYTHON_GC_THRESHOLD` environment variable.  This can be used
+to set the ``threshold0`` value for the garbage collector, similar to calling
+``gc.set_threshold()``.  If the value is empty or ``default``, the default
 threshold value is used.