Fix trailing whitespace in string escaping code

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/ce0fba11-9043-452f-b948-e03c8b644f26

Co-authored-by: xperiandri <2365592+xperiandri@users.noreply.github.com>

Author: Copilot

src/FSharp.Data.GraphQL.Shared/AstExtensions.fs

@@ -110,14 +110,14 @@ type Document with
             for c in s do
                 let appendStr =
                     match c with
-                    | '"' -> "\\\"" 
+                    | '"' -> "\\\""
                     | '\\' -> "\\\\"
                     | '\b' -> "\\b"
                     | '\f' -> "\\f"
                     | '\n' -> "\\n"
                     | '\r' -> "\\r"
                     | '\t' -> "\\t"
-                    | c when c < '\u0020' -> 
+                    | c when c < '\u0020' ->
                         let hex = (int c).ToString("X4", CultureInfo.InvariantCulture)
                         "\\u" + hex
                     | c -> string c