patch 8.2.1602: Vim9: cannot use 'true" with getbufinfo()

Problem:    Vim9: cannot use 'true" with getbufinfo().
Solution:   Use dict_get_bool(). (closes #6873)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 7cc323c..7303db9 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1493,9 +1493,16 @@
   close
 enddef
 
-def Test_gebufinfo()
+def Test_getbufinfo()
   let bufinfo = getbufinfo(bufnr())
   assert_equal(bufinfo, getbufinfo('%'))
+
+  edit Xtestfile1
+  hide edit Xtestfile2
+  hide enew
+  getbufinfo(#{bufloaded: true, buflisted: true, bufmodified: false})
+      ->len()->assert_equal(3)
+  bwipe Xtestfile1 Xtestfile2
 enddef
 
 def Fibonacci(n: number): number