style: format code with Gofumpt and Prettier

This commit fixes the style issues introduced in f44becf according to the output
from Gofumpt and Prettier.

Details: #2733

internal/sync/singleflight/singleflight_test.go

@@ -669,7 +669,7 @@ func TestDoMultipleErrors(t *testing.T) {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-	                v, _, err := g.Do(context.Background(), "key", func(context.Context) (string, error) {
+			v, _, err := g.Do(context.Background(), "key", func(context.Context) (string, error) {
 				atomic.AddInt32(&calls, 1)
 				time.Sleep(10 * time.Millisecond)
 				return "", someErr