Update and pin actions/upload-artifact usage to latest 4.x. These were
previously pointing to @3 which pulls in the latest v3 as they are
released, with the potential to break our workflows if a breaking change
or malicious version on the @3 stream is ever pushed.
Changing this to a pinned version also means that dependabot will keep
this in the pinned 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>