Fix new credo warnings

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/web/proxy/reverse_proxy.ex

@@ -294,20 +294,22 @@ defmodule Mobilizon.Web.ReverseProxy do
     headers
     |> downcase_headers()
     |> Enum.filter(fn {k, _} -> k in @keep_req_headers end)
-    |> (fn headers ->
-          headers = headers ++ Keyword.get(opts, :req_headers, [])
+    |> maybe_keep_user_agent(opts)
+  end
 
-          if Keyword.get(opts, :keep_user_agent, false) do
-            List.keystore(
-              headers,
-              "user-agent",
-              0,
-              {"user-agent", Mobilizon.user_agent()}
-            )
-          else
-            headers
-          end
-        end).()
+  defp maybe_keep_user_agent(headers, opts) do
+    headers = headers ++ Keyword.get(opts, :req_headers, [])
+
+    if Keyword.get(opts, :keep_user_agent, false) do
+      List.keystore(
+        headers,
+        "user-agent",
+        0,
+        {"user-agent", Mobilizon.user_agent()}
+      )
+    else
+      headers
+    end
   end
 
   @spec build_resp_headers(list(tuple()), Keyword.t()) :: list(tuple())
@@ -316,7 +318,11 @@ defmodule Mobilizon.Web.ReverseProxy do
     |> Enum.filter(fn {k, _} -> k in @keep_resp_headers end)
     |> build_resp_cache_headers(opts)
     |> build_resp_content_disposition_header(opts)
-    |> (fn headers -> headers ++ Keyword.get(opts, :resp_headers, []) end).()
+    |> maybe_add_headers_from_opts(opts)
+  end
+
+  defp maybe_add_headers_from_opts(headers, opts) do
+    headers ++ Keyword.get(opts, :resp_headers, [])
   end
 
   @spec build_resp_cache_headers(list(tuple()), Keyword.t()) :: list(tuple())