doc: update sxa's email address to Red Hat from IBM

Signed-off-by: Stewart Addison <sxa@uk.ibm.com>

PR-URL: nodejs#35442
Reviewed-By: Harshitha K P <harshitha014@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Ash Cripps <acripps@redhat.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

.mailmap

@@ -371,8 +371,9 @@ Stefan Bühler <stbuehler@web.de>
 Stephen Belanger <admin@stephenbelanger.com> <stephen.belanger@elastic.co>
 Steve Mao <maochenyan@gmail.com> <maochenyan@msn.com>
 Steven R. Loomis <srloomis@us.ibm.com> <srl@icu-project.org>
-Stewart X Addison <sxa@uk.ibm.com> Stewart Addison <sxa@uk.ibm.com>
-Stewart X Addison <sxa@uk.ibm.com> sxa555 <sxa@uk.ibm.com>
+Stewart X Addison <sxa@redhat.com> Stewart Addison <sxa@uk.ibm.com>
+Stewart X Addison <sxa@redhat.com> sxa555 <sxa@uk.ibm.com>
+Stewart X Addison <sxa@redhat.com> Stewart X Addison <sxa@uk.ibm.com>
 Suraiya Hameed <hameedsuraiya@gmail.com> suraiyah <hameedsuraiya@gmail.com>
 Suramya shah <shah.suramya@gmail.com> ss22ever <ss22ever@users.noreply.github.com>
 Surya Panikkal <surya.com@gmail.com> surya panikkal <surya.com@gmail.com>

README.md

@@ -415,7 +415,7 @@ For information about the governance of the Node.js project, see
 * [starkwang](https://github.com/starkwang) -
 **Weijia Wang** <starkwang@126.com>
 * [sxa](https://github.com/sxa) -
-**Stewart X Addison** <sxa@uk.ibm.com>
+**Stewart X Addison** <sxa@redhat.com> (he/him)
 * [targos](https://github.com/targos) -
 **Michaël Zasso** <targos@protonmail.com> (he/him)
 * [TimothyGu](https://github.com/TimothyGu) -