CTest.UpdateHG: Fix repo URL for local filesystem (#13001)

Use "file:///c:/" instead of "file://c:/" because the latter
looks like a machine:port URL instead of a local file URL.

Tests/CTestUpdateHG.cmake.in

@@ -28,7 +28,7 @@ run_child(
   WORKING_DIRECTORY ${TOP}/repo.hg
   COMMAND ${HG} init
   )
-set(REPO file://${TOP}/repo.hg)
+set(REPO file:///${TOP}/repo.hg)
 
 #-----------------------------------------------------------------------------
 # Import initial content into the repository.