C#: Match Core implementation of `BinToInt` & `HexToInt`

modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs

@@ -106,7 +106,7 @@ namespace Godot
                 instance = instance.Substring(1);
             }
 
-            if (instance.StartsWith("0b"))
+            if (instance.StartsWith("0b", StringComparison.OrdinalIgnoreCase))
             {
                 instance = instance.Substring(2);
             }
@@ -816,7 +816,7 @@ namespace Godot
                 instance = instance.Substring(1);
             }
 
-            if (instance.StartsWith("0x"))
+            if (instance.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
             {
                 instance = instance.Substring(2);
             }