build(deps): bump slackapi/slack-github-action from 1.26.0 to 2.0.0

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 1.26.0 to 2.0.0.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Commits](slackapi/slack-github-action@v1.26.0...v2.0.0)

---
updated-dependencies:
- dependency-name: slackapi/slack-github-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/dependabot-merger.yml

@@ -114,7 +114,7 @@ jobs:
             core.setOutput('pr_list', combinedPRsString);
 
       - name: Post to a Slack channel
-        uses: slackapi/slack-github-action@v1.26.0
+        uses: slackapi/slack-github-action@v2.0.0
         id: slack
         with:
           channel-id: "C03RTLRKJQP"

.github/workflows/sync-readme-changelog.yml

@@ -39,7 +39,7 @@ jobs:
             --data "$payload"
 
     - name: Announce New Release in Slack
-      uses: slackapi/slack-github-action@v1.26.0
+      uses: slackapi/slack-github-action@v2.0.0
       with:
         channel-id: "C063MQJMKJN" #sdk-releases
         payload: |