test: use actual int64 values for LongEnum test spec

Use 2147483648 (int32 max + 1) and 9223372036854775807 (int64 max) to
ensure the int64 branch is properly exercised with values that exceed
int32 range.

Co-authored-by: alexaka1 <22166651+alexaka1@users.noreply.github.com>

Author: Copilot

modules/openapi-generator/src/test/java/org/openapitools/codegen/csharpnetcore/CSharpClientCodegenTest.java

@@ -294,7 +294,7 @@ public void testIntegerEnumJsonConverterUsesNumericOperations() throws IOExcepti
                 "writer.WriteStringValue("
         );
 
-        // Verify long enum uses int64 reader
+        // Verify long enum uses int64 reader with actual int64 values
         File longEnumFile = files.get(Paths
                 .get(output.getAbsolutePath(), "src", "Org.OpenAPITools", "Model", "LongEnum.cs")
                 .toString()
@@ -303,7 +303,9 @@ public void testIntegerEnumJsonConverterUsesNumericOperations() throws IOExcepti
         assertFileContains(longEnumFile.toPath(),
                 "reader.GetInt64()",
                 "writer.WriteNumberValue(",
-                "public static long ToJsonValue(LongEnum value)"
+                "public static long ToJsonValue(LongEnum value)",
+                "AboveInt32Max = 2147483648",
+                "Int64Max = 9223372036854775807"
         );
         assertFileNotContains(longEnumFile.toPath(),
                 "reader.GetString()",

modules/openapi-generator/src/test/resources/3_0/csharp/integer-enum.yaml

@@ -28,13 +28,13 @@ components:
         - Some
     LongEnum:
       enum:
-        - 0
-        - 1
+        - 2147483648
+        - 9223372036854775807
       type: integer
       format: int64
       x-enum-varnames:
-        - None
-        - Some
+        - AboveInt32Max
+        - Int64Max
     DoubleEnum:
       enum:
         - 1.1