Update dawidd6/action-send-mail action to v8 (jenkinsci#26231)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/announce-lts-rc.yml

@@ -17,7 +17,7 @@ jobs:
           discourse-author-username: jenkins-release-bot
           discourse-category: 23
       - name: Post on mailing list
-        uses: dawidd6/action-send-mail@6e71c855c9a091d80a519621b9fd3e8d252ca40c # v7
+        uses: dawidd6/action-send-mail@afe978662944c6805dd197bac88b27acb0bda55a # v8
         with:
           server_address: smtp.gmail.com
           server_port: 465