Fix testsuite RTPOSIXSolver

Update regular expression for new error message from RTPOSIXSolver:

rtposixsolver.c:

silent_cerr("RTPOSIXSolver: sched_setscheduler failed (" << save_errno << ": " << strerror(save_errno) << ")" << std::endl);

parse_mbdyn_error_message.awk:

/^RTPOSIXSolver: sched_setscheduler failed \(1: .*\)$/ { set_error("feature", "RTPOSIX"); }

testsuite/parse_mbdyn_error_message.awk

@@ -192,7 +192,7 @@ BEGINFILE {
     set_error("element", "jointregularization");
 }
 
-/^RTPOSIXSolver: sched_setscheduler failed/ {
+/^RTPOSIXSolver: sched_setscheduler failed \(1: .*\)$/ {
     set_error("feature", "RTPOSIX");
 }