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_clientserver.vim b/src/testdir/test_clientserver.vim
index 152a2e1..eb9fcb8 100644
--- a/src/testdir/test_clientserver.vim
+++ b/src/testdir/test_clientserver.vim
@@ -84,7 +84,7 @@
   call remote_send(v:servername, ":let g:testvar2 = 75\<CR>")
   call feedkeys('', 'x')
   call assert_equal(75, g:testvar2)
-  call assert_fails('let v = remote_expr(v:servername, "/2")', 'E449:')
+  call assert_fails('let v = remote_expr(v:servername, "/2")', ['E15:.*/2'])
 
   call remote_send(name, ":call server2client(expand('<client>'), 'got it')\<CR>", 'g:myserverid')
   call assert_equal('got it', g:myserverid->remote_read(2))
@@ -166,8 +166,8 @@
 
   call assert_fails('call remote_startserver([])', 'E730:')
   call assert_fails("let x = remote_peek([])", 'E730:')
-  call assert_fails("let x = remote_read('vim10')", 'E277:')
-  call assert_fails("call server2client('abc', 'xyz')", 'E258:')
+  call assert_fails("let x = remote_read('vim10')", ['E573:.*vim10'])
+  call assert_fails("call server2client('abc', 'xyz')", ['E573:.*abc'])
 endfunc
 
 " Uncomment this line to get a debugging log