chore(ci): bump golangci-lint to v2.13.1 for go1.27 support

setup-go's "stable" now resolves to go1.27, and golangci-lint v2.12.2
(built with go1.26) panics in go/types with "file requires newer Go
version go1.27". v2.13.0 added go1.27 support. Verified locally:
v2.13.1 runs clean (0 issues) against this tree.