all: don't rebind variables in for loops

See https://tip.golang.org/wiki/LoopvarExperiment#does-this-mean-i-dont-have-to-write-x--x-in-my-loops-anymore

Updates https://github.com/tailscale/tailscale/issues/11058

Signed-off-by: Alex Chan <alexc@tailscale.com>

cmd/tailscale/cli/ffcomplete/internal/complete_test.go

@@ -196,7 +196,6 @@ func TestComplete(t *testing.T) {
 
 	// Run the tests.
 	for _, test := range tests {
-		test := test
 		name := strings.Join(test.args, "␣")
 		if test.showFlags {
 			name += "+flags"