gh-106739: Add `rtype_cache` to `warnings.warn` message when leaked objects found (#106740)

Adding the `rtype_cache` to the `warnings.warn` message improves the
previous, somewhat vague message from

```
/Users/username/cpython/Lib/multiprocessing/resource_tracker.py:224: UserWarning: resource_tracker: There appear to be 6 leaked semaphore objects to clean up at shutdown
```

to

```
/Users/username/cpython/Lib/multiprocessing/resource_tracker.py:224: UserWarning: resource_tracker: There appear to be 6 leaked semaphore objects to clean up at shutdown: {'/mp-yor5cvj8', '/mp-10jx8eqr', '/mp-eobsx9tt', '/mp-0lml23vl', '/mp-9dgtsa_m', '/mp-frntyv4s'}
```

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/Lib/multiprocessing/resource_tracker.py b/Lib/multiprocessing/resource_tracker.py
index ea36950..3783c1f 100644
--- a/Lib/multiprocessing/resource_tracker.py
+++ b/Lib/multiprocessing/resource_tracker.py
@@ -221,9 +221,10 @@ def main(fd):
         for rtype, rtype_cache in cache.items():
             if rtype_cache:
                 try:
-                    warnings.warn('resource_tracker: There appear to be %d '
-                                  'leaked %s objects to clean up at shutdown' %
-                                  (len(rtype_cache), rtype))
+                    warnings.warn(
+                        f'resource_tracker: There appear to be {len(rtype_cache)} '
+                        f'leaked {rtype} objects to clean up at shutdown: {rtype_cache}'
+                    )
                 except Exception:
                     pass
             for name in rtype_cache: