ignore: only stat .jj if we actually care

I was comparing the work being done by fd and find and noticed (with
`strace -f -c -S` calls) that fd was doing a ton of failed `statx`
calls. Upon closer inspection it was stating `.jj` even though I
was passing `--no-ignore`. Eventually I turned up this check in
`Ignore::add_child_path` that was doing stat on `.jj` regardless of
whether the options request it.

With this patch it'll only stat `.jj` if that's relevant to the query.

PR #3212

CHANGELOG.md

@@ -2,6 +2,11 @@ TBD
 ===
 Unreleased changes. Release notes have not yet been written.
 
+Bug fixes:
+
+* [BUG #3212](https://github.com/BurntSushi/ripgrep/pull/3212):
+  Don't check for the existence of `.jj` when `--no-ignore` is used.
+
 
 15.1.0
 ======