[AVR] Fix broken link in README.md (#146821)

Fix broken link

Author: tomtor

llvm/lib/Target/AVR/README.md

@@ -4,5 +4,5 @@ This experimental backend is for the 8-bit Atmel [AVR](https://en.wikipedia.org/
 
 ## Useful links
 
-* [Unresolved bugs](https://llvm.org/bugs/buglist.cgi?product=libraries&component=Backend%3A%20AVR&resolution=---&list_id=109466)
+* [Unresolved bugs](https://github.com/llvm/llvm-project/labels/backend%3AAVR)
 * [Architecture notes](https://github.com/avr-llvm/architecture)