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_cscope.vim b/src/testdir/test_cscope.vim
index 9d12e2f..f4d4208 100644
--- a/src/testdir/test_cscope.vim
+++ b/src/testdir/test_cscope.vim
@@ -189,7 +189,7 @@
 
     " Test: 'cst' option
     set nocst
-    call assert_fails('tag TEST_COUNT', 'E426:')
+    call assert_fails('tag TEST_COUNT', 'E433:')
     set cst
     let a = execute('tag TEST_COUNT')
     call assert_match('(1 of 1): <<TEST_COUNT>> #define TEST_COUNT 50000', a)