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_true_false.vim b/src/testdir/test_true_false.vim
index 37b0997..2071f5e 100644
--- a/src/testdir/test_true_false.vim
+++ b/src/testdir/test_true_false.vim
@@ -40,11 +40,11 @@
     call assert_true(false, 'one in string is true')
   endif
 
-  call assert_fails('if [1]', 'E745')
-  call assert_fails('if {1: 1}', 'E728')
-  call assert_fails('if function("string")', 'E703')
+  call assert_fails('if [1]', 'E745:')
+  call assert_fails('if {1: 1}', 'E728:')
+  call assert_fails('if function("string")', 'E703:')
   if has('float')
-    call assert_fails('if 1.3")', 'E805')
+    call assert_fails('if 1.3")', 'E805:')
   endif
 endfunc