Update troubleshooting-cloudflare-5xx-errors.mdx (#17427)

Changed "Cloudflare returns an Cloudflare-branded" to "Cloudflare returns a Cloudflare-branded"
"an">"a"

Author: mcorreiacf

src/content/docs/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors.mdx

@@ -74,7 +74,7 @@ There are two possible causes:
 
 ### 502/504 from your origin web server
 
-Cloudflare returns an Cloudflare-branded HTTP 502 or 504 error when your origin web server responds with a standard HTTP 502 bad gateway or 504 gateway timeout error:
+Cloudflare returns a Cloudflare-branded HTTP 502 or 504 error when your origin web server responds with a standard HTTP 502 bad gateway or 504 gateway timeout error:
 
 ![Example of a Cloudflare-branded error 502.](~/assets/images/support/image1.png)