Align misuseWithCodable diagnostics with actual macro output

- [x] Update `ConformEncodableTests.misuseWithCodable` to expect four diagnostics.
- [x] Ensure diagnostic IDs, messages, fix-its, and line/column positions match emitted results:
  - [x] Two diagnostics for `@ConformEncodable` at line 1, column 1.
  - [x] Two diagnostics for `@Codable` at line 2, column 1.
  - [x] Mirrors the pattern already used in `misuseWithDecodable`.

Author: qizh

Tests/MetaCodableTests/ConformCodableTests.swift

@@ -38,6 +38,15 @@ struct ConformEncodableTests {
                         .init(message: "Remove @ConformEncodable attribute")
                     ]
                 ),
+                .init(
+                    id: Codable.misuseID,
+                    message:
+                        "@Codable can't be used in combination with @ConformEncodable",
+                    line: 2, column: 1,
+                    fixIts: [
+                        .init(message: "Remove @Codable attribute")
+                    ]
+                ),
                 .init(
                     id: ConformEncodable.misuseID,
                     message:
@@ -491,3 +500,4 @@ struct ConformDecodableTests {
         }
     }
 }
+