Increase timeout for the libcu++ test runs (#1720)

We are getting dangerously close to the timeout, with some CI runs failing already with the last few tests remaining

Given that we have massively increased the number of tests longer test run time is to be expected.

libcudacxx/test/libcudacxx/CMakeLists.txt

@@ -134,6 +134,6 @@ add_test(NAME libcudacxx.test.lit COMMAND
 )
 
 set_tests_properties(libcudacxx.test.lit PROPERTIES
-  TIMEOUT 3600
+  TIMEOUT 4800
   RUN_SERIAL TRUE
 )