chore: bump slackapi/slack-github-action [skip ci] (#375)

Addresses the warning:

> 
Node.js 12 actions are deprecated. Please update the following actions
to use Node.js 16: slackapi/[email protected]. For more
information see:
https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/.

Example run with warning:
https://github.com/cdklabs/cdk-monitoring-constructs/actions/runs/5148341475

---

_By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license_

Author: Eugene Cheung

.github/workflows/release.yml

@@ -140,7 +140,7 @@ project.release.addJobs({
       },
       {
         name: "Send notification",
-        uses: "slackapi/slack-github-action@v1.18.0",
+        uses: "slackapi/slack-github-action@v1.24.0",
         with: {
           payload: `{"html_url": "\${{ steps.get_release.outputs.html_url }}", "tag_name": "\${{ steps.get_release.outputs.tag_name }}"}`,
         },