Fix broken URLs.

Author: NullHypothesis

references.bib

@@ -22,7 +22,7 @@ @inproceedings{Feng2023a
 	booktitle  = {USENIX Security Symposium},
 	publisher  = {USENIX},
 	year       = {2023},
-	url        = {https://www.usenix.org/conference/usenixsecurity23/presentation/feng},
+	url        = {https://www.usenix.org/system/files/usenixsecurity23-feng.pdf},
 }
 
 @inproceedings{Amich2023a,
@@ -31,7 +31,7 @@ @inproceedings{Amich2023a
 	booktitle  = {USENIX Security Symposium},
 	publisher  = {USENIX},
 	year       = {2023},
-	url        = {https://www.usenix.org/conference/usenixsecurity23/presentation/amich},
+	url        = {https://www.usenix.org/system/files/usenixsecurity23-amich.pdf},
 }
 
 @inproceedings{Sun2023a,