patch 8.0.0478: tests use assert_true(0) and assert_false(1) to report errors

Problem:    Tests use assert_true(0) and assert_false(1) to report errors.
Solution:   Use assert_report().
diff --git a/src/testdir/test_perl.vim b/src/testdir/test_perl.vim
index 16fc687..6ef17ad 100644
--- a/src/testdir/test_perl.vim
+++ b/src/testdir/test_perl.vim
@@ -132,7 +132,7 @@
   catch
     return v:exception
   endtry
-  call assert_true(0, 'no exception for `perleval("'.a:expr.'")`')
+  call assert_report('no exception for `perleval("'.a:expr.'")`')
   return ''
 endfunc