fix: use hs2019 instead of rsa-sha256

im not sure why but apparently there's some bug somewhere? maybe some
instances are picky and want the new thing? should still be fine using
sha256 as signing tho

src/server/fetcher.rs

@@ -51,7 +51,8 @@ impl Fetcher for Context {
 
 		let mut signer = HttpSignature::new(
 			format!("{from}#main-key"), // TODO don't hardcode #main-key
-			"rsa-sha256".to_string(),
+			"hs2019".to_string(),
+			//"rsa-sha256".to_string(),
 			&headers,
 		);