build: upgrade to golangci-lint v1.42.0 (#23461)

The new linter version is built with go 1.17 and thus includes the go vet
check for mismatched +build and go:build lines.

Fortunately, no new warnings are reported with this update.

build/ci.go

@@ -330,7 +330,7 @@ func doLint(cmdline []string) {
 
 // downloadLinter downloads and unpacks golangci-lint.
 func downloadLinter(cachedir string) string {
-	const version = "1.39.0"
+	const version = "1.42.0"
 
 	csdb := build.MustLoadChecksums("build/checksums.txt")
 	base := fmt.Sprintf("golangci-lint-%s-%s-%s", version, runtime.GOOS, runtime.GOARCH)