Arrange Admin::BudgetInvestments I18n for buttons under same namespace

config/locales/en/admin.yml

@@ -151,11 +151,11 @@ en:
           unfeasible: Unfeasible
           max_per_heading: Max. supports per heading
           winners: Winners
-          button: Filter
           one_filter_html: "Current applied filter: <b><em>%{filter}</em></b>"
           two_filters_html: "Current applied filters: <b><em>%{filter}, %{second_filter}</em></b>"
         buttons:
           search: Search
+          filter: Filter
         download_current_selection: "Download current selection"
         no_budget_investments: "There are no investment projects."
         title: Investment projects

config/locales/es/admin.yml

@@ -151,11 +151,11 @@ es:
           unfeasible: Inviables
           max_per_heading: Corte por partida
           winners: Ganadores
-          button: Filtrar
           one_filter_html: "Filtro en uso: <b><em>%{filter}</em></b>"
           two_filters_html: "Filtros en uso: <b><em>%{filter}, %{second_filter}</em></b>"
         buttons:
           search: Buscar
+          filter: Filtrar
         download_current_selection: "Descargar selección actual"
         no_budget_investments: "No hay proyectos de gasto."
         title: Proyectos de gasto