vim-patch:8.1.1660: assert_fails() inside try/catch #10472

Problem:    Assert_fails() does not fail inside try/catch.
Solution:   Set trylevel to zero. (Ozaki Kiichi, closes vim/vim#4639)
7780e5c1c5

src/nvim/testdir/test_assert.vim

@@ -1,5 +1,11 @@
 " Test that the methods used for testing work.
 
+func Test_assert_fails_in_try_block()
+  try
+    call assert_equal(0, assert_fails('throw "error"'))
+  endtry
+endfunc
+
 " Must be last.
 func Test_zz_quit_detected()
   " Verify that if a test function ends Vim the test script detects this.