patch 8.2.2944: Vim9: no error when using job or channel as a string

Problem:    Vim9: no error when using job or channel as a string.
Solution:   Be more strict about conversion to string. (closes #8312)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 455a205..a13b0ab 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -4831,10 +4831,11 @@
 		{
 		    typval_T	tv;
 		    char_u	*name;
+		    char_u	buf[NUMBUFLEN];
 
 		    tv.v_type = VAR_JOB;
 		    tv.vval.v_job = iptr->isn_arg.job;
-		    name = tv_get_string(&tv);
+		    name = job_to_string_buf(&tv, buf);
 		    smsg("%s%4d PUSHJOB \"%s\"", pfx, current, name);
 		}
 #endif