style: fix message returned for 404

Co-authored-by: Zaiming (Stone) Shi <zmstone@gmail.com>

apps/emqx_authz/src/emqx_authz_api_sources.erl

@@ -242,7 +242,7 @@ source(Method, #{bindings := #{type := Type} = Bindings} = Req) when
 source(get, #{bindings := #{type := Type}}) ->
     case get_raw_source(Type) of
         [] ->
-            {404, #{code => <<"NOT_FOUND">>, message => <<"Not found ", Type/binary>>}};
+            {404, #{code => <<"NOT_FOUND">>, message => <<"Not found: ", Type/binary>>}};
         [#{<<"type">> := <<"file">>, <<"enable">> := Enable, <<"path">> := Path}] ->
             case file:read_file(Path) of
                 {ok, Rules} ->

apps/emqx_authz/test/emqx_authz_api_sources_SUITE.erl

@@ -183,7 +183,7 @@ t_api(_) ->
 
     {ok, 404, ErrResult} = request(get, uri(["authorization", "sources", "http"]), []),
     ?assertMatch(
-        #{<<"code">> := <<"NOT_FOUND">>, <<"message">> := <<"Not found http">>},
+        #{<<"code">> := <<"NOT_FOUND">>, <<"message">> := <<"Not found: http">>},
         jsx:decode(ErrResult)
     ),