hmac: also support bytearray in 3.7 branch (#9054)

Author: JelleZijlstra

stdlib/hmac.pyi

@@ -23,7 +23,7 @@ if sys.version_info >= (3, 8):
     def new(key: bytes | bytearray, *, digestmod: _DigestMod) -> HMAC: ...
 
 else:
-    def new(key: bytes, msg: ReadableBuffer | None = ..., digestmod: _DigestMod | None = ...) -> HMAC: ...
+    def new(key: bytes | bytearray, msg: ReadableBuffer | None = ..., digestmod: _DigestMod | None = ...) -> HMAC: ...
 
 class HMAC:
     digest_size: int