use ohai headers at the top of search results

Closes Homebrew/homebrew#41832.

Library/Homebrew/cmd/install.rb

@@ -87,9 +87,9 @@ module Homebrew
       else
         ofail e.message
         query = query_regexp(e.name)
-        puts "Searching formulae..."
+        ohai "Searching formulae..."
         puts_columns(search_formulae(query))
-        puts "Searching taps..."
+        ohai "Searching taps..."
         puts_columns(search_taps(query))
 
         # If they haven't updated in 48 hours (172800 seconds), that

Library/Homebrew/utils.rb

@@ -433,7 +433,7 @@ module GitHub extend self
 
   def print_pull_requests_matching(query)
     return [] if ENV['HOMEBREW_NO_GITHUB_API']
-    puts "Searching pull requests..."
+    ohai "Searching pull requests..."
 
     open_or_closed_prs = issues_matching(query, :type => "pr")