fix: grammar correction in resources documentation

Fixed typo "This list not" → "This list is not" in draft specification

Co-authored-by: Claude <[email protected]>

Author: seuros

docs/specification/draft/server/resources.mdx

@@ -348,7 +348,7 @@ Clients can use these annotations to:
 
 ## Common URI Schemes
 
-The protocol defines several standard URI schemes. This list not
+The protocol defines several standard URI schemes. This list is not
 exhaustive—implementations are always free to use additional, custom URI schemes.
 
 ### https://