patch 8.2.0522: several errors are not tested for

Problem:    Several errors are not tested for.
Solution:   Add tests. (Yegappan Lakshmanan, closes #5892)

src/testdir/test_expr.vim

@@ -502,6 +502,7 @@ func Test_funcref()
   call assert_fails('echo funcref("{")', 'E475:')
   let OneByRef = funcref("One", repeat(["foo"], 20))
   call assert_fails('let OneByRef = funcref("One", repeat(["foo"], 21))', 'E118:')
+  call assert_fails('echo function("min") =~ function("min")', 'E694:')
 endfunc
 
 func Test_setmatches()