CTestUpdateSVN: Do not create repo directory first (#13349)

If the directory already exists some svnadmin versions report

 svnadmin: E200011: Repository creation failed
 svnadmin: E200011: Could not create top-level directory
 svnadmin: E200011: '.../CTest UpdateSVN/repo' exists and is non-empty

Tests/CTestUpdateSVN.cmake.in

@@ -41,7 +41,6 @@ init_testing()
 #-----------------------------------------------------------------------------
 # Create the repository.
 message("Creating repository...")
-file(MAKE_DIRECTORY ${TOP}/repo)
 run_child(
   COMMAND ${SVNADMIN} create --config-dir ${TOP}/config ${TOP}/repo
   )