Temporarily add base64 gem

Author: floriandejonckheere

polyphony.gemspec

@@ -31,4 +31,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency  'localhost',            '1.1.10'
   s.add_development_dependency  'debug',                '1.9.1'
   s.add_development_dependency  'benchmark-ips',        '2.10.0'
+
+  # FIXME: remove when all dependencies have bundled base64 (not part of stdlib since Ruby 3.4)
+  s.add_development_dependency  'base64',               '0.2.0'
 end