docs: renames Comodo to Sectigo (#27232)

The certificate authority mentioned "Comodo" has recently been renamed
"Sectigo". This updates the name of the certificate authority, and the
link to get the code signing certificates for Sectigo/Comodo.

docs/tutorial/code-signing.md

@@ -189,7 +189,7 @@ You can get a code signing certificate from a lot of resellers. Prices vary, so
 it may be worth your time to shop around. Popular resellers include:
 
 * [digicert](https://www.digicert.com/code-signing/microsoft-authenticode.htm)
-* [Comodo](https://www.comodo.com/landing/ssl-certificate/authenticode-signature/)
+* [Sectigo](https://sectigo.com/ssl-certificates-tls/code-signing)
 * [GoDaddy](https://au.godaddy.com/web-security/code-signing-certificate)
 * Amongst others, please shop around to find one that suits your needs, Google
   is your friend 😄