ci: add exportloopref linter and upgrade to golangci-lint v1.43.0 (#5281)

`exportloopref` - detects captures of loop variable without
re-assignment

NOTE: There can be false negatives with this linter to avoid being
            overly strict and annoying!

Also upgraded `golangci-lint` to latest (v1.43.0 published 2021-11-03).

pkg/watch/watcher_naive.go

@@ -1,3 +1,4 @@
+//go:build !darwin
 // +build !darwin
 
 package watch

pkg/watch/watcher_naive_test.go

@@ -1,3 +1,4 @@
+//go:build !darwin
 // +build !darwin
 
 package watch

pkg/watch/watcher_windows.go

@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package watch