Fix duplicate records in investments by tag

When an investment had been assigned a user tag and a valuation tag with
the same name, it appeared twice when filtering by tag.

This is because by design, in order to provide compatibility with scopes
using "select" or "distinct", the method `tagged_with` doesn't select
unique records.

Forcing the query to return unique records solves the issue.

spec/helpers/budget_executions_helper_spec.rb

@@ -0,0 +1,17 @@
+require "rails_helper"
+
+describe BudgetExecutionsHelper do
+  describe "#options_for_milestone_tags" do
+    let(:budget) { create(:budget) }
+
+    it "does not return duplicate records for tags in different contexts" do
+      create(:budget_investment, :winner, budget: budget, milestone_tag_list: ["Multiple"])
+      create(:budget_investment, :winner, budget: budget, milestone_tag_list: ["Multiple"])
+      create(:budget_investment, :winner, budget: budget, milestone_tag_list: ["Dup"], tag_list: ["Dup"])
+
+      @budget = budget
+
+      expect(options_for_milestone_tags).to eq [["Dup (1)", "Dup"], ["Multiple (2)", "Multiple"]]
+    end
+  end
+end