fix: use rsa-sha256 for http signatures

peertube (and thus iceshrimp because it uses peertube's lib) seems to
not support hs2019

src/server/fetcher.rs

@@ -43,8 +43,8 @@ pub trait Fetcher {
 
 		let mut signer = HttpSignature::new(
 			format!("{from}#main-key"), // TODO don't hardcode #main-key
-			"hs2019".to_string(),
-			//"rsa-sha256".to_string(),
+			//"hs2019".to_string(), // pixelfeed/iceshrimp made me go back
+			"rsa-sha256".to_string(),
 			&headers,
 		);