unix/main: Enter REPL when inspect active, even with stdin redirected.

This is how CPython behaves.

ports/unix/main.c

@@ -657,7 +657,7 @@ MP_NOINLINE int main_(int argc, char **argv) {
         inspect = true;
     }
     if (ret == NOTHING_EXECUTED || inspect) {
-        if (isatty(0)) {
+        if (isatty(0) || inspect) {
             prompt_read_history();
             ret = do_repl();
             prompt_write_history();