fix(docs): deprecate plat_convert_pk() in v2.9

The deprecation was tagged "Next release after 2.8". Now there is a 2.9
planned, directly use this version.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I0727eebc4a3800dafafc4166b0c2c40a12c90b4b

docs/about/release-information.rst

@@ -67,10 +67,7 @@ after which it will be removed.
 |                                | Date        | after   |                                                         |
 |                                |             | Release |                                                         |
 +================================+=============+=========+=========================================================+
-| plat_convert_pk() function     |   Nov'22    | Next    | Platform conversion to manage specific PK hash          |
-|                                |             | release |                                                         |
-|                                |             | after   |                                                         |
-|                                |             | 2.8     |                                                         |
+| plat_convert_pk() function     |   Nov'22    |   2.9   | Platform conversion to manage specific PK hash          |
 +--------------------------------+-------------+---------+---------------------------------------------------------+
 
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