fix: use each_line iterator; line iterator doesn't exist in ruby 3.0.1. Rename line to line_number

Author: symwell

lib/appmap/trace.rb

@@ -44,10 +44,10 @@ def labels
       private
 
       # Read file and get last comment before line.
-      def self.last_comment(file, line)
+      def self.last_comment(file, line_number)
         File.open(file) do |f|
           buffer = []
-          f.lines.lazy.take(line - 1).reverse_each do |line|
+          f.each_line.lazy.take(line_number - 1).reverse_each do |line|
             break unless (line =~ /^\s*#/) || (line =~ /^\s*$/)
 
             buffer << line.lstrip