pr-pull: fix check conflicts

The previous refactorings broke the conflict check.
Go back to the initially proposed syntax to fill the hashes/arrays,
which is more readable, and which works (the proc syntax does not seem to work for our purpose here)

Remove space before the error message, else only the first line of the output has 2 spaces
and this looks weird

Library/Homebrew/dev-cmd/pr-pull.rb

@@ -369,28 +369,30 @@ module Homebrew
   end
 
   def pr_check_conflicts(user, repo, pr)
-    hash_template = proc { |h, k| h[k] = [] }
     long_build_pr_files = GitHub.search_issues(
       "org:#{user}", repo: repo, state: "open", label: "\"no long build conflict\""
-    ).each_with_object(Hash.new(hash_template)) do |long_build_pr, hash|
+    ).each_with_object({}) do |long_build_pr, hash|
       number = long_build_pr["number"]
       GitHub.get_pull_request_changed_files("#{user}/#{repo}", number).each do |file|
         key = file["filename"]
+        hash[key] ||= []
         hash[key] << number
       end
     end
 
     this_pr_files = GitHub.get_pull_request_changed_files("#{user}/#{repo}", pr)
 
-    conflicts = this_pr_files.each_with_object(Hash.new(hash_template)) do |file, hash|
+    conflicts = this_pr_files.each_with_object({}) do |file, hash|
       filename = file["filename"]
       next unless long_build_pr_files.key?(filename)
 
       long_build_pr_files[filename].each do |pr_number|
         key = "#{user}/#{repo}/pull/#{pr_number}"
+        hash[key] ||= []
         hash[key] << filename
       end
     end
+
     return if conflicts.blank?
 
     # Raise an error, display the conflicting PR. For example: