Doc: fix typo in IncrementalDecoder.setstate (GH-12724)

diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index d2a0c8b..b324637 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -638,7 +638,7 @@
 
    .. method:: setstate(state)
 
-      Set the state of the encoder to *state*. *state* must be a decoder state
+      Set the state of the decoder to *state*. *state* must be a decoder state
       returned by :meth:`getstate`.