patch 8.2.3156: Vim9: term_getansicolors() test fails without +termguicolors

Problem:    Vim9: term_getansicolors() test fails without +termguicolors.
Solution:   Add a check for the feature. (Dominique Pellé, closes #8555)
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index f3e44e3..03bc3fb 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -2217,6 +2217,7 @@
 
 def Test_term_getansicolors()
   CheckRunVimInTerminal
+  CheckFeature termguicolors
   CheckDefAndScriptFailure2(['term_getansicolors(["a"])'], 'E1013: Argument 1: type mismatch, expected string but got list<string>', 'E745: Using a List as a Number')
 enddef