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_search.vim b/src/testdir/test_search.vim
index e06ccaf..93b68a7 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -1494,8 +1494,8 @@
     call assert_fails(";//p", 'E35:')
     call assert_fails("??p", 'E35:')
     call assert_fails(";??p", 'E35:')
-    call assert_fails('g//p', 'E476:')
-    call assert_fails('v//p', 'E476:')
+    call assert_fails('g//p', ['E35:', 'E476:'])
+    call assert_fails('v//p', ['E35:', 'E476:'])
     call writefile(v:errors, 'Xresult')
     qall!
   [SCRIPT]
@@ -1516,8 +1516,8 @@
     call assert_fails('exe "normal /~\<CR>"', 'E33:')
     call assert_fails('exe "normal ?~\<CR>"', 'E33:')
     set regexpengine=2
-    call assert_fails('exe "normal /~\<CR>"', 'E383:')
-    call assert_fails('exe "normal ?~\<CR>"', 'E383:')
+    call assert_fails('exe "normal /~\<CR>"', ['E33:', 'E383:'])
+    call assert_fails('exe "normal ?~\<CR>"', ['E33:', 'E383:'])
     set regexpengine&
     call writefile(v:errors, 'Xresult')
     qall!