[.github/actions/slack-notify] - fix: correct variable for author ema…

…il lookup in Slack notify action (#8976)

- Update the grep search pattern to use the correct environment variable holding the author's name
 - Ensure error messages correctly reference the author's GitHub handle if not found in the authors file

.github/actions/slack-notify/action.yml

@@ -36,8 +36,8 @@ runs:
       run: |
         AUTHOR_NAME="${{ github.actor }}"
 
-        if ! EMAIL=$(grep "^$RAW_AUTHOR: " .authors | cut -d' ' -f2); then
-          echo "GitHub handle $RAW_AUTHOR not found in authors file" >&2
+        if ! EMAIL=$(grep "^$AUTHOR_NAME: " .authors | cut -d' ' -f2); then
+          echo "GitHub handle $AUTHOR_NAME not found in authors file" >&2
           exit 1
         fi
         echo "email=$EMAIL" >> $GITHUB_OUTPUT