twitter: add hashtag normalization test.

Add test for #4243. Also fix warning from bootsnap:

    iseq.rb:18: warning: nested repeat operator '+' and '?' was replaced with '*' in regular expression: /(?<!\A)生誕祭(?:\d+)?\z/

app/logical/sources/strategies/twitter.rb

@@ -20,7 +20,7 @@ module Sources::Strategies
     # The regexes will not match if there is nothing preceding
     # the pattern to avoid creating empty strings.
     COMMON_TAG_REGEXES = [
-      /(?<!\A)生誕祭(?:\d+)?\z/,
+      /(?<!\A)生誕祭(?:\d*)\z/,
       /(?<!\A)版もうひとつの深夜の真剣お絵描き60分一本勝負(?:_\d+)?\z/,
       /(?<!\A)版深夜の真剣お絵描き60分一本勝負(?:_\d+)?\z/,
       /(?<!\A)深夜の真剣お絵描き60分一本勝負(?:_\d+)?\z/,