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>
Pin actions/checkout usage to latest 3.x or 4.x as appropriate. These
were previously pointing to `@4` or `@3` which pull in the latest
versions at these tags as they are released, with the potential to break
our workflows if a breaking change or malicious version for either of
these streams are released.
Changing this to a pinned version also means that dependabot will keep
this in the pinend version format (e.g., referencing a SHA) when it
opens a PR to bump the dependency.
Updates #cleanup
Signed-off-by: Mario Minardi <mario@tailscale.com>