chore(growth): add separated method to merge genders data

This makes easier to test aggregation logic for multiple gender
configuration.

lib/growth/indicators/download.ex

@@ -205,13 +205,17 @@ defmodule Growth.Indicators.Download do
     |> Task.await_many()
   end
 
-  def process_measure(
-        {measure,
-         %{
+  def process_measure({measure, urls}) do
+    urls
+    |> process_genders()
+    |> as_csv()
+    |> save(measure)
+  end
+
+  def process_genders(%{
         female: %{age_tables: female_urls, expanded_tables: e_female_urls},
         male: %{age_tables: male_urls, expanded_tables: e_male_urls}
-         }}
-      ) do
+      }) do
     [
       {:female, :age, female_urls},
       {:male, :age, male_urls},
@@ -221,8 +225,6 @@ defmodule Growth.Indicators.Download do
     |> Enum.map(&Task.async(__MODULE__, :process_gender, [&1]))
     |> Task.await_many()
     |> merge()
-    |> as_csv()
-    |> save(measure)
   end
 
   def process_gender({gender, category, urls}) do