Fix FS1182 compiler warning: mark resolutionFolder as intentionally unused

The resolutionFolder parameter in JsonSchema.parseSchemaFromTextReader is
a placeholder for future JSON Schema $ref resolution support (analogous to
the XML provider which uses this parameter for XSD $ref resolution).
Since $ref resolution is not yet implemented for JSON Schema, the parameter
is currently unused, generating a FS1182 compiler warning.

Prefix it with _ to indicate it is intentionally unused and suppress the
warning, while preserving the future-use intent via the doc comment.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/FSharp.Data.Json.Core/JsonSchema.fs

@@ -231,8 +231,10 @@ module JsonSchema =
     let parseSchemaFromString (schemaString: string) =
         JsonValue.Parse(schemaString) |> parseSchema
 
-    /// Parse a JSON Schema from a TextReader
-    let parseSchemaFromTextReader (resolutionFolder: string) (reader: System.IO.TextReader) =
+    /// Parse a JSON Schema from a TextReader.
+    /// The <c>resolutionFolder</c> parameter is reserved for future <c>$ref</c> resolution support
+    /// and is not currently used; JSON Schema <c>$ref</c> resolution is not yet implemented.
+    let parseSchemaFromTextReader (_resolutionFolder: string) (reader: System.IO.TextReader) =
         let schemaString = reader.ReadToEnd()
         parseSchemaFromString schemaString