Update 8398a7/action-slack action to v3.19.0 (#548)

| datasource  | package             | from    | to      |
| ----------- | ------------------- | ------- | ------- |
| github-tags | 8398a7/action-slack | v3.18.0 | v3.19.0 |

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

Author: renovate[bot]

.github/workflows/notifications.yml

@@ -44,7 +44,7 @@ jobs:
             }
 
       - name: Send Notification
-        uses: 8398a7/action-slack@1750b5085f3ec60384090fb7c52965ef822e869e # v3.18.0
+        uses: 8398a7/action-slack@77eaa4f1c608a7d68b38af4e3f739dcd8cba273e # v3.19.0
         with:
           status: custom
           custom_payload: |