lint: enable intrange linter (#7331)

Enable intrange linter to enforce modern Go range syntax over
traditional for loops, by converting:

for i := 0; i < n; i++

to:

for i := range n

Adding type conversions where needed for compatibility
with existing uint64 parameters.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/pkg/singleflight/singleflight_test.go

@@ -63,7 +63,7 @@ func TestDoDupSuppress(t *testing.T) {
 
 	const n = 10
 	var wg sync.WaitGroup
-	for i := 0; i < n; i++ {
+	for range n {
 		wg.Add(1)
 		go func() {
 			v, err := g.Do(1, fn)