dev-cmd/pr-pull: fail on syntax errors.

This logic was pulled over from `brew pull` where it made sense (as we
wanted to be able to pull broken commits) but doesn't really apply here
where we can easily end up ignoring broken formulae and pushing their
commits anyway.

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

@@ -178,16 +178,12 @@ module Homebrew
     Utils.popen_read("git", "-C", tap.path, "diff-tree",
                      "-r", "--name-only", "--diff-filter=AM",
                      original_commit, "HEAD", "--", tap.formula_dir)
-         .lines.map do |line|
+         .lines
+         .map do |line|
       next unless line.end_with? ".rb\n"
 
       name = "#{tap.name}/#{File.basename(line.chomp, ".rb")}"
-      begin
-        Formula[name]
-      rescue Exception # rubocop:disable Lint/RescueException
-        # Make sure we catch syntax errors.
-        next
-      end
+      Formula[name]
     end.compact
   end