[Doc]: Make nan description more compact.

Signed-off-by: AzizCode92 <azizbenothman76@gmail.com>

Author: AzizCode92

Doc/library/cmath.rst

@@ -338,9 +338,7 @@ Constants
 .. data:: nan
 
    A floating-point "not a number" (NaN) value.  Equivalent to
-   ``float('nan')``.
-
-   See also :data:`math.nan`.
+   ``float('nan')``. See also :data:`math.nan`.
 
    .. versionadded:: 3.6