go.mod: bump staticcheck in prep for Go 1.27, address fallout

Go 1.27 requires this new v0.8.0-rc.1.

But staticcheck 0.8's SA4023 gets stricter and points out that
modifiedExternallyError and handleListenersAccept always return
non-nil errors, and that MonitorHealth's callers don't need a separate
nil check before errors.Is. Simplify all three call sites; no behavior
change.

But then a handful of other places that SA4023 is angry about are
wrong (because it's not considering build tags) and can't be addressed
by ignore directives (again not considering build tags), so we just
disable SA4023 for now.

Updates #20220

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I2fefe3b986b5798c2e01624a0e9820839d21a569