all: fix golangci-lint errors

These erroneously blocked a recent PR, which I fixed by simply
re-running CI. But we might as well fix them anyway.
These are mostly `printf` to `print` and a couple of `!=` to `!Equal()`

Updates #cleanup

Signed-off-by: Will Norris <will@tailscale.com>

cmd/k8s-operator/proxy.go

@@ -311,7 +311,7 @@ func (h *apiserverProxy) addImpersonationHeadersAsRequired(r *http.Request) {
 
 	// Now add the impersonation headers that we want.
 	if err := addImpersonationHeaders(r, h.log); err != nil {
-		log.Printf("failed to add impersonation headers: " + err.Error())
+		log.Print("failed to add impersonation headers: ", err.Error())
 	}
 }