go.mod: re-bump staticcheck to v0.8.0-rc.1

Commit 33042fb97 (go.mod: bump sigs.k8s.io/controller-runtime to
v0.23.3) was based on a stale tree and accidentally reverted the
staticcheck bump from 7eeb62415 back to v0.7.0. That version's IR
builder panics on the Go 1.27 standard library (unexpected expr:
*ast.KeyValueExpr), breaking staticcheck CI on the Go 1.27 test
branch. Everything else in that commit was intentional k8s ecosystem
upgrades; staticcheck was the only collateral revert.

Updates #20220

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I763a3dcc29e592adcf6979c80d6e720b02c0bb09