3.7.26

ci: pin golangci-lint to v2.15.0 and rename the exhaustive map check

golangci-lint 2.15.0 renamed the exhaustive linter's "map" check to
"mapliteral" and rejects the old value at config load. The workflow pulled
"latest" and broke the day after the release. Pin the version so a
release cannot break the build unannounced, and update the config to
match.