Always run receiver regression tests last

This means regression checks for geometry objects etc will run (and
potentially fail) first. This is useful as those regression tests give
more information as to what has gone wrong that the receiver regression
tests.

reframe_tests/tests/mixins.py

@@ -29,7 +29,7 @@ else:
 class ReceiverMixin(GprMaxMixin):
     number_of_receivers = variable(int, value=-1)
 
-    @run_after("setup")
+    @run_after("setup", always_last=True)
     def add_receiver_regression_checks(self):
         reference_file = self.build_reference_filepath(self.output_file)