Issue #21860: Correct docstrings of FileIO.seek() and FileIO.truncate() methods.

Patch by Terry Chia.

--HG--
branch : 2.7
allow archives for rc releases to be built (closes #22484)

--HG--
branch : 2.7
extra : source : 8ce21ffc6df537a7c6eb4f73ef2926121588470f