use the largest prime that can fit in an it

don't hard-code the number in the test

tests/30backend-threadpool.tests

@@ -9,7 +9,7 @@ TEST "Most basic threadpool test" threadpool-basic <<END
 END
 
 TEST "process a function" process-function <<END
-err: the input to the function is 440616
+err: the input to the function is
 err: finished waiting
 END
 

tests/backend/test-threadpool.c

@@ -180,7 +180,7 @@ TEST ("process-function")
 {
   // this is what the scheduler would do once it figures out what function a job needs to run
   LumieraThread t;
-  int number = 440616;
+  int number = 1073676287;
 
   lumiera_threadpool_init();