.github: use and pin slackapi/slack-github-action to latest 1.x (#13554)

Use slackapi/slack-github-action across the board and pin to latest 1.x.
Previously we were referencing the 1.27.0 tag directly which is
vulnerable to someone replacing that version tag with malicious code.

Replace usage of ruby/action-slack with slackapi/slack-github-action as
the latter is the officially supported action from slack.

Updates #cleanup

Signed-off-by: Mario Minardi <mario@tailscale.com>

.github/workflows/govulncheck.yml

@@ -24,7 +24,7 @@ jobs:
 
       - name: Post to slack
         if: failure() && github.event_name == 'schedule'
-        uses: slackapi/slack-github-action@v1.24.0
+        uses: slackapi/slack-github-action@37ebaef184d7626c5f204ab8d3baff4262dd30f0 # v1.27.0
         env:
           SLACK_BOT_TOKEN: ${{ secrets.GOVULNCHECK_BOT_TOKEN }}
         with:

.github/workflows/test.yml

@@ -559,7 +559,7 @@ jobs:
       # By having the job always run, but skipping its only step as needed, we
       # let the CI output collapse nicely in PRs.
       if: failure() && github.event_name == 'push'
-      uses: ruby/action-slack@v3.2.1
+      uses: slackapi/slack-github-action@37ebaef184d7626c5f204ab8d3baff4262dd30f0 # v1.27.0
       with:
         payload: |
           {
@@ -574,6 +574,7 @@ jobs:
           }
       env:
         SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+        SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
 
   check_mergeability:
     if: always()