patch 8.2.1593: tests do not check the error number properly

Problem:    Tests do not check the error number properly.0
Solution:   Add a colon after the error number. (closes #6869)
diff --git a/src/testdir/test_put.vim b/src/testdir/test_put.vim
index 6741af1..3d4c5e7 100644
--- a/src/testdir/test_put.vim
+++ b/src/testdir/test_put.vim
@@ -60,16 +60,16 @@
   setlocal nomodifiable
 
   normal! yy
-  call assert_fails(':put', 'E21')
-  call assert_fails(':put!', 'E21')
-  call assert_fails(':normal! p', 'E21')
-  call assert_fails(':normal! gp', 'E21')
-  call assert_fails(':normal! P', 'E21')
-  call assert_fails(':normal! gP', 'E21')
+  call assert_fails(':put', 'E21:')
+  call assert_fails(':put!', 'E21:')
+  call assert_fails(':normal! p', 'E21:')
+  call assert_fails(':normal! gp', 'E21:')
+  call assert_fails(':normal! P', 'E21:')
+  call assert_fails(':normal! gP', 'E21:')
 
   if has('mouse')
     set mouse=n
-    call assert_fails('execute "normal! \<MiddleMouse>"', 'E21')
+    call assert_fails('execute "normal! \<MiddleMouse>"', 'E21:')
     set mouse&
   endif