[3.12] Add measuring unit to sys.getswitchinterval docs (GH-130457) (#130459)

Add measuring unit to `sys.getswitchinterval` docs (GH-130457)
(cherry picked from commit 89d8b2d)

Co-authored-by: sobolevn <[email protected]>

Author: miss-islington

Doc/library/sys.rst

@@ -870,7 +870,7 @@ always available. Unless explicitly noted otherwise, all variables are read-only
 
 .. function:: getswitchinterval()
 
-   Return the interpreter's "thread switch interval"; see
+   Return the interpreter's "thread switch interval" in seconds; see
    :func:`setswitchinterval`.
 
    .. versionadded:: 3.2