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

(cherry picked from commit 48428bd087cfc084df0e9ada32a4e89d85083ef6)

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

@@ -107,7 +107,7 @@ namespace Godot
                 instance = instance.Substring(1);
             }
 
-            if (instance.StartsWith("0b"))
+            if (instance.StartsWith("0b", StringComparison.OrdinalIgnoreCase))
             {
                 instance = instance.Substring(2);
             }
@@ -817,7 +817,7 @@ namespace Godot
                 instance = instance.Substring(1);
             }
 
-            if (instance.StartsWith("0x"))
+            if (instance.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
             {
                 instance = instance.Substring(2);
             }