fix test: use builtin pager instead of less, revert to warn for all missing pagers

tests/integration_tests.rs

@@ -1458,6 +1458,7 @@ fn env_var_bat_paging() {
 fn basic_set_terminal_title() {
     bat()
         .arg("--paging=always")
+        .arg("--pager=builtin")
         .arg("--set-terminal-title")
         .arg("test.txt")
         .assert()