style: fix import ordering and restore nil-body comment

- Reorder stdlib imports in review_test.go to alphabetical (goimports convention)
- Restore explanatory comment for nil body in DeleteReview

Addresses review comments #20533, #20534 on PR #119

github/review_test.go

@@ -2,9 +2,9 @@ package github
 
 import (
 	"context"
-	"fmt"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"strings"

github/reviews.go

@@ -221,6 +221,7 @@ func (c *Client) DeleteReview(ctx context.Context, owner, repo string, number in
 	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/reviews/%d",
 		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number, reviewID)
 
+	// nil body: the GitHub DELETE endpoint for reviews requires no request body.
 	_, err := c.doRequestWithBody(ctx, http.MethodDelete, reqURL, nil)
 	if err != nil {
 		var apiErr *APIError