Update .github/workflows/nightly-contract-tests.yml

Co-authored-by: semgrep-code-launchdarkly[bot] <167133144+semgrep-code-launchdarkly[bot]@users.noreply.github.com>

Author: tanderson-ld

.github/workflows/nightly-contract-tests.yml

@@ -43,7 +43,7 @@ jobs:
       - nightly-contract-tests
     steps:
       - name: Send Slack notification
-        uses: slackapi/slack-github-action@v2.1.0
+        uses: slackapi/slack-github-action@8eec7b3b943e15be5302493bb90a15bafa6973c6 # v2.1.0
         with:
           webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
           webhook-type: incoming-webhook