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_winbuf_close.vim b/src/testdir/test_winbuf_close.vim
index 3f67e88..1d3e357 100644
--- a/src/testdir/test_winbuf_close.vim
+++ b/src/testdir/test_winbuf_close.vim
@@ -27,7 +27,7 @@
   " test for failing :rew when hidden not set
   set nohidden
   call setline(1, 'testtext 2 2')
-  call assert_fails('rewind', 'E37')
+  call assert_fails('rewind', 'E37:')
   call assert_equal('Xtest2', bufname('%'))
   call assert_equal('testtext 2 2', getline(1))
 
@@ -66,7 +66,7 @@
 
   " test ":edit" failing in modified buffer when 'hidden' not set
   call setline(1, 'testtext 3 3')
-  call assert_fails('edit Xtest1', 'E37')
+  call assert_fails('edit Xtest1', 'E37:')
   call assert_equal('Xtest3', bufname('%'))
   call assert_equal('testtext 3 3', getline(1))
 
@@ -80,7 +80,7 @@
   split Xtest3
   set nohidden
   call setline(1, 'testtext 3 3 3')
-  call assert_fails('close', 'E37')
+  call assert_fails('close', 'E37:')
   call assert_equal('Xtest3', bufname('%'))
   call assert_equal('testtext 3 3 3', getline(1))
 
@@ -115,7 +115,7 @@
   call assert_equal('Xtest2', bufname('%'))
   quit!
   call assert_equal('Xtest3', bufname('%'))
-  call assert_fails('silent! quit!', 'E37')
+  call assert_fails('silent! quit!', 'E37:')
   call assert_equal('Xtest1', bufname('%'))
 
   call delete('Xtest1')