Don't parse diffs on renamed files

On renamed files, the 'diff' key of a file in a sourcediff structure is
not defined.

Co-authored-by: Saray Cabrera Padrón <scabrerapadron@suse.de>

src/api/app/services/sourcediffs_parser.rb

@@ -6,7 +6,9 @@ def initialize(sourcediffs:)
   def call
     @sourcediffs&.each do |sourcediff|
       sourcediff['filenames']&.each do |filename|
-        content = sourcediff['files'][filename].dig('diff', '_content')
+        next unless sourcediff['files'][filename].key?('diff')
+
+        content = sourcediff['files'][filename]['diff']['_content']
 
         sourcediff['files'][filename]['diff']['parsed_lines'] = DiffParser.new(content: content).call
       end