fix bug in retina detector (#5255)

Signed-off-by: Can Zhao <canz@nvidia.com>

Fixes #5250.

### Description

Fixed bug that allow_low_quality_matches in set_regular_matcher was
always set to True and it's not using value from the argument, in
retinanet.

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [x] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

Signed-off-by: Can Zhao <canz@nvidia.com>
Signed-off-by: monai-bot <monai.miccai2019@gmail.com>
Co-authored-by: monai-bot <monai.miccai2019@gmail.com>

Author: Can-Zhao

monai/apps/detection/networks/retinanet_detector.py

@@ -318,13 +318,17 @@ def set_regular_matcher(self, fg_iou_thresh: float, bg_iou_thresh: float, allow_
         Args:
             fg_iou_thresh: foreground IoU threshold for Matcher, considered as matched if IoU > fg_iou_thresh
             bg_iou_thresh: background IoU threshold for Matcher, considered as not matched if IoU < bg_iou_thresh
+            allow_low_quality_matches: if True, produce additional matches
+                for predictions that have only low-quality match candidates.
         """
         if fg_iou_thresh < bg_iou_thresh:
             raise ValueError(
                 "Require fg_iou_thresh >= bg_iou_thresh. "
                 f"Got fg_iou_thresh={fg_iou_thresh}, bg_iou_thresh={bg_iou_thresh}."
             )
-        self.proposal_matcher = Matcher(fg_iou_thresh, bg_iou_thresh, allow_low_quality_matches=True)
+        self.proposal_matcher = Matcher(
+            fg_iou_thresh, bg_iou_thresh, allow_low_quality_matches=allow_low_quality_matches
+        )
 
     def set_atss_matcher(self, num_candidates: int = 4, center_in_gt: bool = False) -> None:
         """