Fix memory leak in IIS StartupHook by properly disposing PhysicalFileProvider (#63322)

* Initial plan

* Fix memory leak in IIS StartupHook by properly disposing PhysicalFileProvider

Co-authored-by: danmoseley <6385855+danmoseley@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: danmoseley <6385855+danmoseley@users.noreply.github.com>

Author: Copilot

src/Servers/IIS/IIS/src/StartupHook.cs

@@ -49,8 +49,10 @@ public static void Initialize()
             var iisConfigData = NativeMethods.HttpGetApplicationProperties();
             var contentRoot = iisConfigData.pwzFullApplicationPath.TrimEnd(Path.DirectorySeparatorChar);
 
+            using var fileProvider = new PhysicalFileProvider(contentRoot);
+
             var model = ErrorPageModelBuilder.CreateErrorPageModel(
-                new PhysicalFileProvider(contentRoot),
+                fileProvider,
                 logger: null,
                 showDetailedErrors: true,
                 exception);