patch 8.2.1183: assert_fails() checks the last error message

Problem:    assert_fails() checks the last error message.
Solution:   Check the first error, it is more relevant.  Fix all the tests
            that rely on the old behavior.
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index 85312ae..ae7e301 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -559,7 +559,7 @@
   call assert_equal(1, found)
 
   call assert_fails("call job_stop('abc')", 'E475:')
-  call assert_fails("call job_stop(job, [])", 'E474:')
+  call assert_fails("call job_stop(job, [])", 'E730:')
   call assert_fails("call job_stop(test_null_job())", 'E916:')
 
   " Try to use the job and channel where a number is expected. This is not
@@ -1641,15 +1641,15 @@
   call assert_fails("call job_start('ls', {'in_top' : -1})", 'E475:')
   call assert_fails("call job_start('ls', {'in_bot' : -1})", 'E475:')
   call assert_fails("call job_start('ls', {'channel' : -1})", 'E475:')
-  call assert_fails("call job_start('ls', {'callback' : -1})", 'E475:')
-  call assert_fails("call job_start('ls', {'out_cb' : -1})", 'E475:')
-  call assert_fails("call job_start('ls', {'err_cb' : -1})", 'E475:')
-  call assert_fails("call job_start('ls', {'close_cb' : -1})", 'E475:')
-  call assert_fails("call job_start('ls', {'exit_cb' : -1})", 'E475:')
+  call assert_fails("call job_start('ls', {'callback' : -1})", 'E921:')
+  call assert_fails("call job_start('ls', {'out_cb' : -1})", 'E921:')
+  call assert_fails("call job_start('ls', {'err_cb' : -1})", 'E921:')
+  call assert_fails("call job_start('ls', {'close_cb' : -1})", 'E921:')
+  call assert_fails("call job_start('ls', {'exit_cb' : -1})", 'E921:')
   call assert_fails("call job_start('ls', {'term_name' : []})", 'E475:')
   call assert_fails("call job_start('ls', {'term_finish' : 'run'})", 'E475:')
   call assert_fails("call job_start('ls', {'term_api' : []})", 'E475:')
-  call assert_fails("call job_start('ls', {'stoponexit' : []})", 'E475:')
+  call assert_fails("call job_start('ls', {'stoponexit' : []})", 'E730:')
   call assert_fails("call job_start('ls', {'in_io' : 'file'})", 'E920:')
   call assert_fails("call job_start('ls', {'out_io' : 'file'})", 'E920:')
   call assert_fails("call job_start('ls', {'err_io' : 'file'})", 'E920:')