triagebot: enable issue transfer (#14874)

I think it's pretty common for a lint to be proposed for clippy only for
consensus to be it belongs in rustc, and additionally sometimes bugs get
filed here when the fault is actually with rustc.

https://forge.rust-lang.org/triagebot/transfer.html#issue-transfer

changelog: none

Author: flip1995

triagebot.toml

@@ -15,6 +15,8 @@ allow-unauthenticated = [
 
 [close]
 
+[transfer]
+
 [issue-links]
 
 [mentions."clippy_lints/src/doc"]